What Causes Swelling And Itching In Anal Opening?

I am 18 female and have been having this problem a few months,,,,I randomly notice a small bubble like something coming out of my rear end. sometimes when i go to the bathroom sometimes not, can be itchy.. it doesn't bother me much when it happens, its always random. usually everyday, it is often swelling in different areas of the inside ring..as if there is some sort of abscess liquid inside the skin up (?) . Hope u can help!, getting kind of annoying, thanks!