Misses Period??

I had unprotected sex almost 5 weeks ago and i started bleeding durning sex which i have had sex before but i never bled full on an this happened twice already it bleeds a lot the after like a few minuets it stops! and i have missed my period for a week now which i dont feel any pregnacy symptoms and i have been doing that vitamin c 6000mg a day for around 4/5 days and my period still hasnt come!? + i have always got my period on time! am i starting to have irregular periods or !?? help please!