What is wrong with my Digestive system?!

What is wrong with my Digestive system?

I have always watched what i ate as a teen i weighed 160 and am almost 6' i gained 80 pounds and now have lost 30 i go up and down in weight and can not maintain. I am working out and have been put on a restricted diet of 4 proteins 3 veggies 2 starches and 3 fruits. And i am working out up to 6 hours a week. but i go off my diet and i gain 5 pounds in a week. i stay on and i loose 1 or 2. Also with thge restricted calories and food i can only intake a certain amount of fiber. And sometimes it will be 4-5 days until i have a bowel movement. I have researched it and i am doing everything- eating high fiber breads eating 1 tablespoon of "good fat" veggies- i have even tried laxatives-- NOTHING WORKS! It is very annoying to be worrying about it constantly. The only way i have ever lost a good amount of weight before is not eating. I am trying to avoid this. But this diet is so slow! and screwing my digestive system up. Any thoughts?

I don't know what kind of "doctor" put you on that diet but look for a nutritionist or dietitian who know what they are doing.
you are definitely not eating enough and when you deprive your body all you lose is water weight and muscle and slow down your metabolism, instead of losing you are also gaining fat. No wonder you gain it all back because of false "weight" loss!!!
Body needs 70cal/hour just for basic functioning for people who are over 150lbs and that's 1680cal/day (i guess your "doctor" doesn't know that)
dont use regular laxatives - use glycerin suppositories
when you are gona stop starving your body your digestive system is gona work fine.
find daily calorie intake calculator on the net, enter all your stats and it will tell you how many calories you need a day to maintain, take off 300-400cal off that number and that's how much you need to lose.
eat 5-6 small meals a day (eat every 2-3 hours - it optimizes your metabolism)
5-8 servings of fruit and veggies a day
8 glasses of water
have complex carbs for breakfast - they give you energy
have protein (lean meat, legumes etc) for dinner - repairs muscle
cardio is the only fat burning exercise and burns fat all over your body (running, jogging, swimming, spinning, elliptical etc) 4-6 times a week for 30-50min (ideally 45min because the first 20-30min body burns carbs and only then starts burning fat), light weight training (more muscle=faster metabolism)
dont consume foods that are made of white flour (white bread, cakes, pasta etc.), sugar loaded foods (cookies, icecream, candy etc) and nothing fried, oily.
ofcourse you can spoil yourself once in a while with a little treat:)