I'm sorry you're suffering with this. I actually meant to reply when you first posted but forgot oops!
But you could try (as I think was already mentioned) a medicated nasal spray which needs no prescription and isn't very expensive. I had a truely horrible sinus infection when ds2 was only a few months old & fully bf, I put up with it for ages and tried many natural methods and couldn't get rid of it. When I finally saw my gp he said to try the spray and it was wonderful! He also said the bizolvon (sp?) I'd been taking wouldnt hurt and should help loosen (my thinking in the first place lol). Just also try and spend a lot of time with your head down because that's the way the sinuses need to be to drain fully you may already know, a book or even laptop on the floor between feet works quite well. PS lots and lots of fluids so any mucous there won't be so thick.
Hope you find some relief really soon!