Earlier quoted context omitted.
Wow. Which antibiotic(s)? I've found that I don't generally get a noticeable therapeutic effect until near the end of the antibiotics course with sinusitis.
Maybe it wasn't a sinus infection? I hate the damn things because they're a lot like a cold and it seems like the recommendation is "if you're still miserable after 2 weeks, maybe you should go to a doctor". Then you discover that you could have been feeling better days ago...
I always complained to the docs that the antibiotics took too long to have a noticeable effect, to which more than one replied that there was limited blood flow to where the infection is, thus it took longer to clear.