I doubt the probiotic is causing the weight loss. Probiotics are just bacteria strains. Your weight loss is probably due to your UC. However, based on the information you have provided it's hard to know how sick you are. In my case I lost a lot of weight, 25lbs, in my last flare. I didn't feel sick during the weight loss phase and just assumed that my exercise routine had kicked up my metabolism. It wasn't until about 6 weeks into the weight loss that my UC symptoms went from moderate to severe. Anyway, my weight loss was caused by UC, not the exercise.
dx proctitis in 1987
dx UC in 1991, was stable until 1998
1998 started prednisone, asacol, pentasa, nortriptylene, ativan, 6MP, rowasa enemas and suppositories, hydrocortisone enemas, tried the SCD diet, being a vegetarian, omega 3s, flax, pranic healing, yoga, acupuncture, probiotics
2000 lost all my B-12 stores and became anemic
2001 opted for j-pouch surgery- now living life med-free