My stomach hurts, could i have the flu?

last week my stomach hurt and the next morning i had a very large bowel movement and felt better. A couple of days later I felt sick again and could only poo a little at a time and they were like pebbles, so I took a amagneesium citrate drink and had diarrhea cuz I was constipated. Now, 3 days later I still feel bad and still have some diarhea. I have been on Phentermine and stopped taking it when I was constipated, cuz it will sometimes do that, and I am not prego. Could I have the flu? It is just my stomache and i never checked my temp.