You should be tested at 3 months' post exposure, and then again at 6
months.  That will catch the overwhelming majority of positives.

If you really wish to be compulsive, you can get tested another six
months after that (1 year post exposure).

What you need to think about is what you were you doing, why you were
doing it and how you can avoid doing it again.  One way is to remember
how you feel at the moment.

B/