what can I do for a persistent belly ache?

After taking medicine for a sinus infection a couple weeks ago I have had a persistent belly ache. I saw the Pa. yesterday,she put me on nexium instead of my regular omeprazole,last night,I had the worst doubled over belly ache for 5hours .97.9 temp… It’s still here but not as bad. What can I eat?
I burping after everything.

Omeprazole or Nexium pill is used to treat acid reflux, heart burn or hyperacidity. You mentioned you are taking this for sinus infection?
Abdominal pain, burping is the side effect of the drug. Discontinue the pill and consult doctor.