I lost my virginity yesterday, i got my period last night really heavy lots of cramps & back pain. is that normal?

Most likely normal: The two events, the heavy period and the episode of intercourse, are probably not related. You probably would have had a heavy period even if you didn't have intercourse. Best wishes!

Normal if hymen tear: Bleeding can occur when the ring around the entrance of the vagina is torn at first intercourse or from injuries within the vagina with "rough" sex. Cramping can occur with a "period" and if it was time for your period can be normal. Cramping and bleeding can occur with a polyp or fibroid inside the uterus lining which gets stimulated or from the cervix. If this continues you should get examined.

Most Likely: I am presuming your partner used a condom. The first time sexual experience, the so-called sexual debut, can be an emotional experience and may cause some physical discomfort in the genital area.