What could this be?

I was due to get my period yesterday. I had a very small amount of frank red blood in my cm.

I decided to put in a tampon because I thought I was going to get my period. When I took the tampon out it was just a small amount of brown on the tampon and there hasn’t been anything since.

I vomited last night and had really bad heartburn. Maybe I’m just getting sick and that’s delaying my period?