Hello, I understand that you took medication for a sinus infection that caused stomach pains. Inflammation of the sinus is known as sinusitis. Common cold, deviated septum, rhinitis, and nasal polyps can cause this. There are two types of sinusitis:

a) Acute sinusitis: inflammation of the tissues lining the sinus that usually lasts less than three weeks.

b) Chronic sinusitis: Inflammation of the sinus that is chronic in nature lasting more than three weeks.

Such patients usually present with runny nose, facial fullness, nasal congestion, fever, and cough. In regard to your question, antibiotics can cause clostridium infection which may present with abdominal pain, diarrhea. Certain antibiotics such as penicillin, cephalosporin, and clindamycin group can cause clostridium infections. The abdominal pain may be due to an ulcer, gastritis, pancreatitis that has to be properly evaluated. I would suggest you to get a set of investigations such as Endoscopy, CT abdomen, serum amylase and lipase to rule out the above-mentioned diseases. It is best that you do not use the remaining medication has it causes stomach pains and consult your doctor regarding the change of medication. You can also get the reports to rule out any infection. Hope this helps. Thank you.