What Causes Swelling Of Lymph Nodes?

my lymph nodes were a tad bit swelled the other day so I did some research and as we know research can sometimes scare us right? anyhow, I was just wondering if you have been exposed to a virus, like HIV for instance, how long do your lymph nodes stay swollen? mine were swollen for about 2-3 days and they weren t visible but I can feel the irritability. and when I put pressure on them to check, I felt it even more.