Dont know if you know this already, but:
Not finishing your antibiotics doesnt affect just you. By science-magic (sorry, i dont know how else to explain it), your personal cooties as well as their all their children and relatives floating around out there develop a resistance to that antibiotic, making it less effective for anyone in the entire world who is prescribed that antibiotic, not just you.

So yeah we would encourage you to prioritize finishing your antibiotics. I know it gets yucky towards the end of the scrip, you can smell them in your pee like they were not processed, but this letting your sinus infection get halfway better then flare up again, may be okay for now (which it isnt really), but in the future you may contract another infection (esp given all your past surgeries) that they will have a hard time taking down.