24 yr f, always only had 1 bm every 3-4 wk still have to take laxitive, eat only healthy, +fobt, colonscopy only showed hemerrhoids, what could it be?

Chronic constipation: As hard as it is to believe, if this has been your lifelong pattern, it is the pattern you are stuck with. If you want to go more frequently ( you didn't mention any discomfort) you should use a blend of laxatives including fiber -30grams/day- a stool softener, an osmotic and perhaps a mild stimulant. Drink 8 glasses of water/day and exercise. If no one has checked TSH it is a consideration.

Not enough: Fluids and excessive caffeine and or alcohol. You need to eat properly with adequate fiber and drink a minimum of 80-100 ounces of caffeine free/alcohol free fluid daily.