3 months will give you a conclusive result.
Anal sex is very risky. Even protected anal is risky because the condom is more likely to break. But aside from that the odds are 1 in 10,000 of the person even having it. Then being a top is slightly safer.
The test only told you that you didn't have it three months prior. So don't believe anyone that tells you there safe because they got tested. Unless they haven't had sex in three months. The anxiety is causing your problems, but it can be a good lesson.