Synthia, I do not have this problem but since I work at a hospital, I see young people that do. The first advice you should have is to see a GI doctor–someone who specializes in gastroenterology for help with this since it is such a major problem in your life. There are milk products in a lot of non-dairy items and if you are really very lactose intolerant, it might help to try lactase pills in addition to avoiding dairy. I remember some people using fiber to “thicken” stool–either as bran or maybe Citracel. One thinks of bran for constipation, but it also can help for diarrhea since it absorps water.
WithHope for a cure of these diseases
Addendum. I looked in the Merck Manual Home Edition for advice for fecal incontinence and it also first said that ways to form the stool such as fiber are usually the first step. It also suggested exercising the pelvic muscles to help retrain them. This may not work. For diarrhea, there were a few other suggestions–to look at the amount of fruit and fruit juice consummed, to think about magnesium in antiacids or sorbitol in sugar-free products, and also caffeine as a cause. Lots of people today drink sugar-free colas and these can be the culprit.
Finally, search for IBS in the forum search feature and there may be other suggestions. WithHope