Is this irritable bowel syndrome or .. any ideas?

For about a year or longer now I have been having problems with abdominal pain and diareoh immediately after eating/ 15 min to 1 hour after. It doesn't seem to make any difference what I eat and can also happen when I havent actually yet eaten. It makes me worried to eat outside as when it happens the need for the loo is very urgent. I dont eat before I go out or go to work as I have had it on the way there and had to rush home . Also when it happens my bpwel doesnt completely empty so then i have the diareoh again later after the first one after eating. I dont know if it would be anything to do with this but I feel very tired most of the time , have problems with getting to sleep, randomly feel dizzy/lightheaded during the day, have muscle and joint pain especially in my neck/shoulders/lower legs/feet. My mum had myotonic dystrophy/muscular dystrophy and I am 20.