There are certain times in a pregnancy where you shouldn't have sex especially near the end as it can cause the uterus to contract and you could have a premature delivery. You'd have to go to your doctor to be sure but this is what I found and apparently unless under specia circumstances you can have sex all along (although don't assume your gf is going to want it!)
is oral sex safe?
Yes, normal oral sex won't harm you or your baby and many consider it a good solution if intercourse is deemed too risky. But during pregnancy blowing air into the vagina could be dangerous. Even if this is the first time you've heard of such a practice, we're mentioning it because blowing hard could cause an air embolism (obstructing a blood vessel) and is potentially dangerous for mother and baby.
Can I have sex while i'm pregnant?
Absolutely. With a normal pregnancy, you can keep doing it right up until your waters break. Do check with your doctor or midwife first if you're having any problems with your pregnancy, such as placenta preavia or bleeding, or if you have a history of miscarriages.

Will sex harm the baby?
You won't hurt the baby by making love, even with your partner on top. The thick mucus plug that seals the cervix helps guard against infection. The amniotic sac and the strong muscles of the uterus also protect your baby. Though your fetus may thrash around a bit after orgasm, it's because of your pounding heart, not because he knows what's happening or feels pain. There are some important circumstances, however, in which you may be advised not to have intercourse.