diarrhea without weight loss

I have had diarrhea since November last year, I went to china on holiday, the diarrhea started there and I have had it ever since. My doctor is not concerened because I have not lost any weight and the sample they tested did not have bacterial infection. BUT it is so difficult to cope with, some times it is just water that comes out, and I feel drained, I have to carefully plan my eating around trips out of the house and I am really hungry. Someone sugested it might be parasites so i bought soemthing to do a flush, with black walnut, wormwood and clove in it, the diarrhea stopped almost at once and I have a blissful month, then about a week after stopping the parasite stuff the diarrhea is back, it makes no difference what I eat or leave out, starving only stoped it as long as i wasn't eating, I have no pain, just the runs, but I am getting very tired of it. Going on holiday to America next month, thinking of getting more of the parasite stuff just so i can eat and go out normally while I am there, but does anyone have any ideas for me what this can be?? I have been back to the doctor, but like I siad she isn't bothered because I am not loosing any weight.