Hi , The Last Couple Days I Been Experiencing Stomach

Hi , the last couple days I been experiencing stomach pains. Yesterday I went to the ER, the doctor said I most likely have gastritis and gave me different medicine on the spot. Doctors also gave me a prescription for it as well. I visited my PCP this morning, he gave a test(results back by Monday) and scheduled a sonogram. Now I have swelling on my sides right above my hipbone. I went back to my PCP he didn't sound to worried and said it might be backed up stool. Should I be concerned about the swelling ? Or it might be a side effect from all the different drugs at the hospital?