Period late on Letrozole but bfn?

I’m wondering if anyone else has had this happen to them. My period is 2 days late on my fourth round of letrozole 5.0mg. Since the first month I started it my period’s been 28 days apart like clockwork. I’m currently on cycle day 30 and it’s 12 dpo according to my app. I know I did successfully ovulate because during my follicle scan there was free fluid around my ovary and my progesterone was 15.7 one week later. Usually by now I would have gotten my period. The only thing I can think that might have messed things up is I had strep last week and got a Bicillin shot.

Either way this is driving me nuts. I just want to start my period or have a positive pregnancy test. Has anyone else had something similar happen to them???