please someone help me understand!

So I'm currently 4 days late on my period...It's extremely odd to me because I'm always regular.Up until this month where I've been having unprotected sex for 2 months now and we're ttc.So this is pretty exciting.Although something very odd is happeneing...

I'm having no PMS or pregnancy symptoms...I normally get PMS a week before my period.. the normal (Backache,Sore boobs,Cramps,etc)I've had none..Only thing I be had this past week is headaches,Frequent urination,and fatigue and tiredness.)I had a little nausea the past couple weeks.I wonder why this could be.Even if I'm not pregnant and supposed to get my period why am I not getting my normal PMS??!Im super confused 🤷‍♀️ I took 2 dollar tree pregnancy tests yesterday both came back negative.I don't know what's going on cause I'm not stressed at all!What should I do?