Empty sac

Hi ladies! My husband and I tried to get pregnant for about a year without any luck. I track my periods and ovulation very closely. We got pregnant but it unfortunately ended in a chemical. Two months later we got pregnant again and we were so excited. I went for an ultrasound at what I thought was 6+3 based on LMP. Unfortunately, all that that he saw was an empty gestational sac. He has schedule me for a follow up ultrasound on the 15th. I’m so concerned because I have been tracking everything so closely. Has anyone else had something similar happen? Thanks ladies!