The thing about laxative abuse is that it often makes the body have difficulty in having BMs on its own. Since you are taking so many laxatives a day, I would broach the subject with a doctor, preferably one experienced in treating people with EDs.
Fiber can keep people regular, but many don't realize that if you increase your fiber intake drastically all of a sudden and don't increase your water intake, it makes constipation worse. My husband has anal fissures and has to be on a high fiber diet, so I hear about his problems all the time in glorious detail

You don't want to go from eating about 5 g of fiber a day to over 30 g of fiber in a day; that will definitely cause constipation. You have to ease into it. Probably, in the end, your goal should be around 30 g a day--high fiber foods include beans (black beans, kidney beans, pinto beans, sweet peas), oatmeal, bran, berries (especially the berries--you wouldn't think it, but look it up online--blackberries, blueberries, strawberries, raspberries), some cereals have lots of fiber too like All Bran or Kashi has a lot of high fiber cereals.
It is key when you increase your fiber intake to drastically increase your water intake. Be sure you are getting around 10 8 oz. glasses of water daily with that much fiber.
I would also recommend you consult a doctor about your situation. Ask if it is safe to add a magnesium supplement to your diet; that may help you, but don't take the magnesium without consulting a doctor. Since you have been abusing laxatives for so long, I think it would be a good idea for you to get your electrolytes checked to be sure that nothing is too out of balance and life threatening. Then, if your electrolytes are OK, ask the doc. if it is safe to take a small magnesium supplement during the transition off laxatives. Please don't take the magnesium while on laxatives, it will exacerbate the laxative effect and could be dangerous if your electrolytes are very imbalanced.
Good luck!