Batz

I am 26 years old and for the passed week my stools have been up and down. I am constantly running to the bathroom. One mintue I'll have long soft stools and the next I'll have a bout of diarreha. Their either dark brown or a dark green color. Some times it will go on about 3-4 times a day and other times it will be about 2 times a day. I feel like I have this lump in my throat and I am constantly burping. I tried taking Pepto-Bismal and it doesnt seem to be helping. I tried Nexum too and thats not working either.I discussed this with my doctor and he says try Pepcid Ac, I did and I still feel like crap.

any suggestions on what i can do or what may be going on with me?