Steven,
After you have been sick with a viral infection (like the flu), you can get a secondary infection in your sinuses. In order to get rid of this, you have to get an antibiotic to take. Either a Z pack or a 10 day supply of amoxicillin, or one of the other ones that you take for 10 days. The Z packs are nice because you only have to take them for 5 days. Another thing to invest in is a neti pot. You can buy one in Walgreens or CVS. You mix kosher salt with very warm water in order to melt the salt, and you pour it through both sides of your nose. It goes into one nostril and comes out the other. Then you do it in your other nostril. It really cleans out your nose. If I use it religiously, (like every morning) I never get a cold. Salt water kills a lot. I bought my neti pot on ebay and mine is called a rhino horn neti pot. You sound to me like you have a secondary infection. Hope this helps.