Might my girlfriend be pregnant?

A few weeks ago, my girlfriend and I laid in her bed together naked. She performed oral sex on me and all of the sperm went into her mouth going no where else. The tip of my penis touched her clitoris but it has never been inside her whatsoever. She is on birth control pills to regulate her period for a little while and she was supposed to start on Sunday and it is Monday night. I know she hasn't done a good job of taking the pill regularly. It isn't a high strength pill, just enough to regulate periods and such. I have fingered her before but there was never any sperm on my fingers and I have no clue what is going on. Should I wait a bit longer for the period or should I really start wondering? Lastly, isn't a glob of sperm required in order for it to fertilize the egg considering it needs a fluid to travel through? Please respond soon, I am truly worried about this and I need help. It is nearing the end of my freshman year in high school and I truly need some guidance! Please reply soon!