Fertility doctor

Today my husband and I went to the fertility Dr for the first time while ttc for two years. To start, they wanted to do blood work and a transvaginal ultrasound to make sure everything looked good. She says my uterus, endometrium lining and ovaries look great! Then right at the end she moved it just right and there was something interfering with the endometrium lining. If she moved down there was a black blob that separated the lining in half but in all other views it look like one thin line. She then asked if I have heavy periods which I dont...they're regular and heavier the first day and light the rest of it. What could this mean? Have any of you encountered this?!