Missed Period

I have just recently been referred for IVF treatment due to the fact I have endometriosis and how long me and my husband have been trying. But this month I have not come on my period. I am 3 days late but my periods are usually like clock work...day 28 and I bleed but this month...NOTHING. I've not even had any pre-bleed leading up to it and this is freaking me out as I've heard this could effect us doing IVF if my periods are being weird? I have also done 3 pregnancy tests and all say NOT PREGNANT. Has anyone had anything similar happen? I had an ectopic pregnancy back in 2015 where my tube ruptured and I was internally bleeding but this pregnancy wasn't detected til the point in which it became life threatening. Help please 😔