Sex before period & pregnancy

If you have sex before your period (about 2-3 days before) and the condom slips off and you don't notice until the end. If you still get your period on time 2-3 days later are you in the clear, or could the whole "implantation" thing still happen during the period or right after? Would the period have not happened even though it was so close and I was already feeling pms/cramps that week? I know there is no way to know for sure without a test but I'm just wondering if a test would be a waste of time. Still went through normal period, but the accidental unprotected sex only happened a couple days before so I don't know. I feel no symptoms but it would be to soon to tell anyway. This was only about 2 weeks ago. I guess I can only wait and see until next months period but just wanted to hear what anyone else had to say?