Diarrhoea. I should be worried about?

I was having loose motions for about 3-4 weeks. I tried having norflox TZ but it didn't work. So I went to a physician, who gave me Ray PP (something like that, probably a probiotic capsule), metrogyl, and one other tablet to have over the course of 5 days. I followed the course and felt better, getting rid of loose motions. Now after about a week or so of completing my course, I've started having loose motions again for the past 1 week. I consumed food from an outside stall, which I believe is the cause for this. I tried having oats and cutting on milk and felt a little improvement in my condition. Should I take the same medicines again, or norflox TZ, or should I just make changes to my diet and see if that helps me? Is there any other condition that I should be worried about?