Period period where are you!?!

I stopped my diet about one month ago, never lost my period while on my diet, btw. I’ve gained back maybe 3 pounds which is probably water weight since stopping. Also drastically increased my water intake, protein and started taking an iron supplement twice per day since stopping my diet.

My period is now 3 days late. My period is never late. I have taken 4 pregnancy tests including two first response tests... all negative. We use condoms as birth control. I don’t use any sort of artificial hormones.

Any ideas why I may be behind? I’m 32 btw.