Meanwhile, inside the uterus, the lining is getting thicker as the hormones that the follicular cyst is producing (estrogen) cause the endometrial
lining to grow. This is all to prepare
for a pregnancy. Right before menstruation, the
lining is quite thick indeed.
then when a pregnancy does not occur, the lining sloughs. that is called menstruation.
so for you, if your are right before menstruation, that ultrasound could be completely normal.