I have been having unprotected sex with my boyfriend for about a month (not smart, I know) and on the 31st of jan I had a period. (I rarely ever have regular periods, in fact, I don't normally have one. Its usually 5-6 months apart) it ended the 6th of feb, and me and him continued to have sex and then on the 15th of feb, I had another period. What does this mean?

Maybe it's nothing, but I would certainly get a pregnancy test!

Its possible that it is completely normal for you. However, it couldn't hurt to visit your ob/gyn, get an exam, just in case.