Sinus infection help?

I think I have a sinus infection, but I’m not quite sure. It’s been going on 2 weeks now, started with a cold, and has lots of sneezing and pepper-nose still (which, I thought sinus infections didn’t have, that they were more about pressure – which, I don’t have). But, I have to blow my nose every couple of minutes. Dayquill/Nyquill also help, which I thought they didn’t if it was a sinus infection.

So, question: a) is this a sinus infection? b) anything I can do other than keep blowing, sinus rinsing, and taking Dayquill? c) what exactly does a sinus rinse do for a infection, anyway? Because I do it, and I feel better for like 30 seconds, but then the mucus flood starts again and I have to blow my nose again. d) if sinus rinses are all I can do, how often am I supposed to do them for an infection?