stands for human chorionic gonadotropin
. It is a hormone that is produced by chorion of the placenta. The good news for you is that any level below 5 mIU/L is negative for pregnancy
. Thus, your girlfriend is not pregnant.
Further, If you are going to engage in regular sexual intercourse, I recommend that you use OCP pills as a method of contraception
. Also, I recommend that you use condoms along with them to reduce the chances of pregnancy. I hope this helps. Best of luck.