Severe Sinusitis; Anti-Biotics don't seem to work

Hello fellow sinusitis sufferers!

I'm a 33-year old Caucasian Male, work out regularly (weights and bike) and generally feel well most of the time. However, since I was maybe 10 years old I keep getting nasty Sinus infections. Tiny little cold turns into a struggle with congestion, fever, colored discharge and so on and so forth. This year alone it has happened twice: once in January (I took Amoxicillin 1500mg/day for 10 days and it seemed to help) and a few days ago. I again am taking Amoxicillin (same dosage), but nothing happens and I do mean it. I am extremely congested, my eys hurt, my throat is sore, my headache is constant and i can't sleep at night and so on and so forth. All the wonderful sympthoms of a sinus infection~

I tried drinking water with Apple Cider Vinegar and Grapefruit Seed Extract throughout the day (seems a common remedy online) and using water and seasalt solution to drain my nose, but again to no avail. If things do not improve over the course of the day (and I'm sure they won't), I will go see a doctor.

I guess my question is this: is it possible that my body has developed tolerance for Amoxicillin and thus it no longer helps? Any advice/help is appreciated!

Thanks in advance