My period is being weird.

Tana

So my period is acting funny. I am 4 or more days late I'm not pregnant as I went to the hospital a few days ago for extreme pain in my right ovary and they told me I wasn't pregnant, but my body is acting like I'm currently on my period. To recap I'm not on my period but my body seems to think so and I'm having pain near my ovaries and I am not pregnant. What could be going on?