Late period. 4 days. TTC

I have a normal cycle of 28-31 days for the past 2 years (that I've been keeping track of) every month I can literally feel when it comes. I do have sore boobs, mild cramping but no period, I keep thinking "this is it" and its not there. I dont have any new stress or medications in my life, besides those and pregnancy, what can the cause be? Yes I am TTC. I haven't done a test yet.