I wouldn't use anything OTC without a medical doctor's OK. Too much stuff out there ends up making us worse.
The problem with sinus infections is that they are often not cured with one round of antibiotics. You should expect to need a second round, maybe with something different, to clear it up.
You should have a list of antibiotics that you don't tolerate and your reactions. Give this to the doctor and your pharmacist. Lots of antibiotics given are the same group - like Avelox, which gives me hives, is in the Cipro group. So I can't take anything from the Cipro group.
Amoxicillin is often given for sinus infections, but I find I need something else after a week or so. It starts to do the work, but doesn't kill off everything. I usually am prescribed a sulfa drug to finish off. It's really hard to get drugs into the sinuses as there isn't a good blood flow and the cavities are large.
Although claims abound, colloidal silver is not effective against bacteria. It delivers only metallic silver. You have to use the silver ion as in silver sulfadiazine - for which you need a prescription.