You need to speak with your doctor, as I bet you've got more questions than this. It seems your education in this area is sorely lacking.
However, to answer a few questions.
- Women can become pregnant with one act of sexual intercourse. The likelihood depends on when it is in her cycle (e. g. did she just have her period? Then it's less likely but not impossible), your sperm count and the motility and overall health of your sperm.
- Have oral sex pretty much whenever you please (not on the bus, of course). It's generally safe but if the pregnancy is high risk (e. g. she is first pregnant at a rather late age, say, after turning 40), there can be questions but those are better answered by her OB/GYN.
- Condoms are not 100% effective in preventing pregnancy. They are good (and they are a lot better than nothing) but they are not perfect. And this even means condoms used correctly, every single time, and they do not break.
- Oral sex is generally fine during a woman's entire pregnancy but again, check with her doctor in order to be certain (hell, you can usually have sex during pregnancy, but again, check as there are some conditions where it is not advisable). Do not have oral sex in the delivery room.