Cramps, Diarrhea, Pale Stools, Normal Blood Tests, Back Pain. Had Food Poisoning. What Should I Do?

Hello, I ve recently suffered food poisoning from a Mexican Restaurant. The following morning I had severe cramps and diarrhea . I went to my doctor the following Friday after my next movement appeared pale in color. He perscribed me antibiotics. All my blood tests came back normal. After a week of the antibiotics, I found my lower abdominal area to be dry (coming off the perscription), and I developed constipation after two days of being normal. My passings were regular in color, but they were round in shape and hard to pass. To combat the constipation, I started taking probiotics and fiber supplements . After three days of taking this I had two bowel movements and they were pale in color again. After the passings my stomach is increasingly tender, and I am experiencing some back pain. What should I do? And what you guess be a possible diagnosis?