Why do I keep missing my period??!

Krista

For the last 4 months now my period has been messed up usually being over a week late and or only lasting a day or two. This month I had some bleeding during intercourse 6 days after my period was due and that’s it! My period is now 12 days late. I’m not on any birth control or medications and havnt been very stressed. I started doing daily ovulation tests about a week ago to try to figure out some pattern but all have been negative so far and all pregnancy tests are negative as well...