I know you posted some time ago and I assume you have resolved the issue by now. But it is VERY unlikely that you could have gotten her pregnant. Nature makes it easy, but not THAT easy. It is true that precum CAN include some sperm, especially if you are approaching a second ejaculation and you haven't urinated between them to "clear the system" so to speak. But rubbing your genitals together, even bathing her clitoris in your precum is highly unlikely to get her pregnant. In fact, even if you actually ejaculated all over her vulva and clitoris, the chances are greater, but still low. There are all kinds of hazards and roadblocks for the sperm to reach their target (which is why you ejaculate so many of them each time), so the miniscule number that might possibly be in your precum would literally have an "uphill" battle to get deep enough inside her to make her pregnant. HOWEVER, if she is all wet from you (and herself), then do be careful about slipping fingers into her vagina, as you COULD push any sperm present toward your cervix.
As for oral sex as you describe it ... passing actual CUM back and forth could be a problem if you then go down on her. If she merely had your precum in her mouth and passed it to you, and so on, tongues don't really have that much of a reach, so the chances are pretty low that you could get her pregnant that way. Possible, yes, but very low. The interior environment of her vagina is designed to actually make it hard for the sperm to survive very long. This is kind of an elegant method of ensuring that only the strongest, healthiest, and most vigorous sperm get to the target. And any number of other factors can give her irregular periods. She should speak to her gynecologist, as that could be a symptom of something even more serious needing her (and your) attention.