Before anyone points it out, I know I'm an idiot, and deserve all the suffering I may get. Anyway: I've been with my girlfriend for 2 months, I'm 18, she's 15, neither of us had had sex before. We both wanted to wait until she's at least 16 (age of consent here) and till we're both more settled. The other night however, we were cuddling in bed, and I had an erection since we were both kinda horny, she then gave me a blowjob until I came in her mouth, she swallowed and there was no cum left anywhere. A couple of minutes later, after I'd regained my erection, she straddled me, then grabbed my dick. She said "I just want to try it a bit", I thought when she said that, she was gunna brush her pussy against my cock or something, but to my surprise, she slipped straight down on me, and my cock slid all the way in. As soon as it went all the way in, she stood up and withdrew my cock from her because of her experiencing a sharp pain due to her first penetration. 4 days later, her period hasn't come on time (it hasn't in 4 months though) and she is feeling quite sick and achy, especially on her breasts (though she has mastitis), she also has had some heartburn. Although all of these things happen to her sometimes, it's really worrying that they're all happening now, and may suggest she's pregnant. My question is, how high are the chances of her being pregnant off just one entrance of my penis into her vagina, considering I'd already cum shortly before, and had it all cleaned up? And is it possible the symptoms she's showing is down to her being on her period / already being slightly ill? Opinions and your experiences would be most appreciated.