I have been with the same parntner for over a year now and usually if there is a little blood during sex I start my period the next day, but this time I still havnt started and am not supposed to start for a week due to me being on the pill. We have had sex since then and no blood though, so if anyone could help explain this is would be great.
It could be due to the pill or it could be that your body has just got used to the sex so it doesn't bleed anymore. Hope this helps :)