When you are pregnant in the first trimester your body produces a hormone called HCG. The amount of HCG doubles every two days. When you have an abortion, it is an abrupt stop to a natural process of your body. It takes some time (the amount of time varies from person to person) for your body to stabilize itself and for the HCG levels to fall. This is why if you take a pregnancy test after an abortion it might read positive.
As for becoming pregnant right after an abortion, it really just depends on the woman. To become pregnant you have to ovulate. As you know, sometimes because of stress your body will skip ovulation, this would cause you to not be able to become pregnant. I’m not a doctor but it would not seem any more likely to become pregnant after an abortion.
It is clear since you had an abortion that this is not a good time for you to become pregnant. My suggestion is that you stop having sex. If you don’t want to become pregnant not having sex is the only way to ensure that you won’t.
Birth control and condoms are not effective 100% of the time. Any time you have sex there is always a chance for pregnancy and there is always a chance to get a sexually transmitted disease.
Have you ever considered waiting until you are married to have sex? Maybe this is something that you have thought about before. Waiting until you are married is the best decision you can make for your body and for your life. There is a lot less heartache.
I would encourage you rather than just going on birth control and running the risk of getting pregnant again, to slow down and consider waiting until you are married for sex.