If your still really worried then see another Doctor, don't wait for your next period esp if your bleeding whilst having sex. Was it your first time? or had you only had sex a couple of times as your hymen may not have broken properly as this can cause bleeding in first time sex.
(sorry I am assuming your young and apoligise if this isn't the case)
It could always be your hormones causing your periods to act so irrationally or could even be the stress of worrying what is wrong that's making them act so haywire!
Seek different meical advice if your not satisfied.