It’s easy to not think twice about your bowel habits until suddenly things don’t flow the way they usually do. The best way to ease constipation is to figure out what’s causing it in the first place. Some cases of constipation can be fixed by taking in more fiber and water. However, there can be underlying causes for your gastrointestinal backup that you didn’t see coming ― and that won’t necessarily be fixed with more fiber and water. Know this: Most people deal with constipation here and there. “Constipation is extremely common,” said Dr. Ketan Thanki, a colorectal surgeon at the MemorialCare Todd Cancer Institute at Long Beach Medical Center in California. “Almost everyone experiences it at some point in their lives.” Unfortunately, the risk of chronic constipation, which is when you have symptoms of constipation that last for three months or more, increases as you age. If you’re suddenly grappling with constipation, it’s fair to wonder what’s behind it. If a lack of fiber and water don’t seem to be the culprit, consider these surprising causes of constipation:You’re not getting enough sleep.This is a big one. Research suggests that insomnia, poor sleep quality, and not sleeping long enough all raise your risk of constipation. There are a few reasons for this, according to Dr. Stephanie A. McAbee, a gastroenterologist and assistant professor of medicine at Vanderbilt Health. “Sleep deprivation disrupts normal colonic function,” she said. Your colon operates on a 24-hour circadian rhythm, and that includes regulating the movement in your gut, McAbee explained. Your gut tends to be more active in the morning and slow down at night ― lack of sleep can throw this cycle off, raising the odds you’ll get stopped up.Not getting enough sleep impacts your gut-brain axis and increases your body’s production of stress hormones like cortisol, noted Dr. Jeremy Polman, a gastroenterologist at Northwell’s Lenox Hill Hospital. Unfortunately, higher cortisol levels are linked to constipation, he said. You’re using antihistamines.Your allergy treatment may be throwing off your gut health. Antihistamines have anticholinergic effects, which means they suppress the parasympathetic nervous system, reducing involuntary muscle movements and functions like your digestion, McAbee explained. That can also reduce gut motility, or how fast things move through your gut. “These anticholinergic effects can also include dry mouth and urinary retention,” McAbee said. This isn’t true of all antihistamines, though. “Newer antihistamines such as loratadine, cetirizine and fexofenadine are less constipating,” Thanki noted.You’re taking calcium supplements.While calcium supplements can support your bones, they may also slow down your gut motility.“Calcium supplements, especially those containing calcium carbonate, decrease smooth muscle contractions in the gut wall, and bind to fatty acids and bile acids, making them less soluble and decreasing their lubricating effects within the gut,” Thanki said. They also decrease how much fluid your gut secretes, leading to harder poop, he added. You keep ignoring the urge to go.There are certain times when you just can’t poop, like when you’re sitting in traffic or stuck in a big meeting. But constantly ignoring your body’s urge to use the bathroom can end up stopping you up, according to McAbee.“Repeatedly ignoring the urge to defecate contributes to constipation through maladaptive learning and altered rectal sensation,” she said. Not only that, when stool sits in your colon for long periods of time, your colon starts to reabsorb water from the stool, Polman explained. “This will make the stool dry and hard, which can lead to constipation,” he said. You’re on iron supplements.Like calcium, iron supplements can interfere with your gut’s normal function. Higher levels of iron can irritate your gut mucosa ― the moist lining ― and slow down the motility of your colon, McAbee explained. “Oral iron supplements can create hard, bulky, dry stool, which is constipating,” Polman said.You’re dealing with anxiety or depression.Having anxiety or depression can impact your gastrointestinal tract through the gut-brain axis, McAbee said. “The prevalence of constipation is nearly twice as high in people with a history of depression and anxiety vs. without,” she said. There are a few reasons for this, like activation of your fight or flight response, side effects from medications to treat anxiety and depression, and less physical activity due to these conditions, according to Polman. Kinga Krzeminska via Getty ImagesIf you think you're drinking enough water and eating enough fiber, talk to your doctor about reasons for your constipation.Here’s how to get relief from constipation:Doctors recommend starting out by making sure you’re taking in enough fiber and water. Everyone’s needs are different, but it’s generally recommended that adults take in 25 to 34 grams of fiber a day. (Pale yellow urine is a sign that you’re well hydrated.) “You could consider adding kiwis to your diet, as these have been shown to improve constipation,” Polman said. From there, make sure you’re getting at least seven hours of sleep a night and at least 150 minutes of moderate-intensity exercise a week, he said. “If you’re still constipated, check your current medication side effects and see if any can cause constipation,” Polman noted. If that still doesn’t work, you can try osmotic laxatives like polyethylene glycol or milk of magnesia, according to McAbee. “If stool consistency remains problematic, the next step is to add a stimulant laxative ― bisacodyl or glycerin suppositories,” she said. If you continue to struggle or if constipation is a regular thing for you, McAbee said, it’s best to consult with a gastroenterologist for an evaluation. “While occasional constipation is quite common, anyone who experiences an abrupt change in bowel habit or constipation with any ‘alarm signs,’ such as rectal bleeding or unexplained weight loss should seek immediate care to assess for other more serious health issues,” she said.