Me and my boyfriend had unprotected sex 4 times in the same day and he finished inside. Today my period has stopped but I still have the cramping like I normally do. Is there a possibility of pregnancy? Or does having sex during this time slow down your cycle and is it going to come back? I'm very worried and scared about this.. any help would be greatly appreciated.

Pregnancy is always possible, any time during your cycle, with birth control or not - it's all a matter of probability. But if you fall in the small % group, (say 5% during your period, but that is just a guesstimate), you are still 100% pregnant when the other 95% of women are 100% not pregnant.
So stop worrying and get on the pill, patch, or IUD.

No having sex will not normally change your period or cycle. Yes you can get pregnant,

You will not know for another month till you either get ( or not get ) your next period.

If you are going to be having sex, get on birth control and use a condom both.