You better check to see who the father is!
Just kidding, everyone is different but I am willing to bet that 1.5 months is not enough to kill your Sperm count to 0. I have been on HRT (hormone replacement therapy) for about 2 years now, and about 1/2 way through the wife wanted a kid. Had a sperm count and it was 0! While you are taking Test, your body will stop producing sperm. I wouldn't say that there is a ZERO percent chance of pregnancy while you are taking it or that it is just as or more safe than a condom, but if its your wife, you could sleep at night not having to wonder about it. But it will take more than just an occasional cycle to get it down enough.
Now on the bright side, the Doc switched me from Test Enthalate to HCG and then Clomid and it brought my count back up to above normal. She had her wish about 3 months after switching. Now we are just waiting to make sure that the pregnancy is good before I go back to HRT and weekly Test injections.