important girl talk

since my last period I've had unprotected sex with three different guys. I know how it sounds and I've heard it all. I need to be more responsible and careful when it comes to anything sexual. my period was supposed to be yesterday and now I'm one day late. I'm going to a clinic tomorrow and they're going to check me for pregnancy and STD's and put me on birth control. if they say I'm pregnant, how would I find out who the dad is? can they give me a date of fertilization this soon? or will I have to wait? I'm extremely scared and during the past weekend some things happened that shouldn't have and its really been a wake fup call for me. I don't have a lot of people to talk to about this and I had to get it out. if any of you girlies have any stories similar or any words of encouragement or advice please share!