Can you have sex when you have your period? If so, how?

I'm 14 years old and a virgin. When I explore myself or masturbate I find that I can fit at least 3 fingers inside myself without much discomfort. I haven't had sex and yet it feels like I'm stretched out or something. Could this mean that I really am just loose? I mean I've been fingered by my boyfriend before but never anything else.
Shouldn't my hymen be intact? My friend told me that the heavier your period flow is how wideset you are *downthere*. What could she mean by that? I'm so confused and embarrassed that I don't know better. Please help.

Is there anything other than birth control that will help lighten my period and relieve cramps?