I don't know about septra, but I just finished amoxicillin and it threw my stomach off. I had my gastritis under control with prevacid and carafate and diet, but after the antibiotics I was a mess. Nausea, stomachaches, always feeling like I had to go to the bathroom, tons of gas and bloating both upper and lower and agnawing hunger like feeling that it was hard to distinguish from feeling sick or hungry.
I am still not feeling too well. My symptoms of gastritis and IBS are in full swing. I am just taking my meds and eating things like you. Rice, chicken, jello, applesauce without sugar (I use Mott's natural applesauce because the only ingredients are apples and water, no acid.), toast, cheerios, oatmeal, animal crackers. Comfort foods I guess. I had plain cheese pizza over the weekend, BIG mistake. Today has been a miserable day and yesterday too. Hope this helps of gives you more ideas of what to eat. I had chicken noodle soup and toasted (grilled) cheese today. That seemed to go okay so far.