How old are you and your girlfriend?
Has she had her periods before?
If not, it could be the start of her periods.
Or, if so, ask her if the blood or pain is any different to her period\
She's 16 and I'm 15, she had her period 2 days ago which I thought was the case. She said she hasn't had the kind of cramps at that kind of level of pain and the blood wasn't as heavy as her normal period.
Wait?? You are 15,and you are fingering her with 3 fingers?
If it was her hymen it would only have lasted a couple of mins if you did scratch her she should go to the doctor if she is still bleeding like that, if the blood is any different from her period she deffinitly should go.