I agree with Tivo, if he penetrated you with his penis, then you have lost your virginity. Not everybody bleeds when they lose their virginity or experience pain (I didn't). Also, some people believe you are still a virgin if the guy did not ejaculate, but this is not the true meaning of it.
Sure it has a lot to do with the sex that you had!
Anytime a male penetrates you and ejaculates inside you your taking a big chance of getting pragnant and that will surely mess up your period... period.
even if you guys use PROTECTION (CONDOMS) thats not always 100% they can tear/break break...or come off.
I'm not sure how old you are but if your going to have sex like this be sure and go see your Dr and get on B.C.
Meh, some people have irregular cycles. All the new hormones from having sex probably threw yours out. It should even up as your body gets used to it or you might stay irregular. This is why I'm on the pill, I always know when it's going to be and it always works.
for the first quesitons... no, technically you are not a virgin anymore. Even if he only penetrated you for 30 seconds. You lost your virginity the moment his penis entered your vagina.
the second question.. are you sure it was a full period? Was it light spotting or a full blown period? If it was light spotting then you were probably still bleeding a bit from the sex (your hymen was broken). If it was a full period, then I don't think sex would have effected it. I'd lean more towards your body being irregular. I know my period took a while to regulate itself. Does that sound like a possibility, or have you always been pretty dead-on with when you get it?