missed regular period ?

So I have regular periods after I got my mirena removed. I have an ovulation and <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a>. It always starts when it says it will. But today I hav had no period and haven't even had my periodcramps. I took a first response and it was negative. Any opinions?