I have a swollen painful bump on my nostril is it a cold sore? I've had it for 3 days and doesn't have a head like a pimple. It's very red and painful

A good history. A good social and medical history would be helpful to try to pinpoint what you may have. It is certainly likely that you have a cold sore, but I am more inclined to believe that you have a simple pimple in that area. I have seen several like this, they tend to get very red, no visible head on the skin surface, and very painful.
May be. You may indeed have a cold sore. Is there tingling too? These are symptoms of a cold sore. However, it may be something entirely different. Please see your dermatologist to make the proper diagnosis and if it is a cold sore, you can start the proper treatment.