I've had on on sharp pain on left side of abs toward back. i've been fighting a sinus infection close to a month..on 3rd try of antibiotics-thoughts?

Pull muscle w cough?: If you've been coughing a lot with the sinus infection it's possible you pulled a rib muscle.

Need more info: Three rounds of antibiotics given by whom? Probably would benefit by seeing ENT doctor for this sinus problem. There are adjuncts to therapy that may help to clear your problem. Do not know what the abdominal problem is, but hope it is not a complication of the antibiotics. You should discuss with the ENT doctor. If you are already seeing one it might be a good idea for second opinion.