What Causes Abdominal Pain Along With Diarrhea?

Hii. I m a male 18 years old and I m hitting th gym from the last 6months without any problem, but all of a sudden , I m having abd pain and loose motions , but after I consulted a doctor with some medications I was all well, but still suffering from loose motions , specially when I eat anything. My elders say it might be a swollen stomach from inside .,,..... is it so?????????