Sinus infections are miserable. Personally, I would wait until your infection has run its course. You may feel better (or worse, depending on the type of bacteria) when you first start the antibiotics, but you could suppress your immune sytem by adding more stressors (i.e, weight lifting). If that happens you will be set back even further.
My advice, rest and water, water, and more water. As far as the contraindications for antibiotics, it depends what type of drug (cephalosporins, penicillins, macrolides, tetracyclines, ect). I seriously doubt that MAG-10 will cause an interaction with an antibiotic. I have taken androgens with antibiotics in the past without incident.
The drugs that bodybuilders will find adversely effect antibiotics are aspirin and loop diuretics. However, I am not a doctor, just a nurse practitioner student. I hope this helps.