Cramps, late period

Jessa • Unofficial nomad. Aspiring midwife. Fierce lover of naps.
My period hasn't been regular at all the last couple of months, in fact I missed a total of 3 months a while back. This time, my period is 5 days late and I've had pretty severe cramps. What's going on? Why am I having cramps but no period?
Glow keeps giving me statistics on endometriosis based on the information I've put in, is that what this is??
Definitely no chance of being pregnant.