It is possible to miss it in an ultrasound... BUT what did the blood work say? You were not totally clear about this...
I would seek another opinion, it could be that rather than being undeveloped eggs that it could have been cysts. For wome with poly-cystic ovarian syndrome (PCOS) it would not be uncommon to miss periods.
Given the info you provided, chances are the ultrasound in conjunction with the bloodwork was accurate. Depending on when yout LMP was in March, you would be anywhere from 5-8 weeks along, plenty enough time to at least see a sac if you were pregnant.
Again, I would ask for a second opinion or at least see if they do not suspect pregnancy as the cause of your missed period, find out what they think could be causing it.
Andi