Any advice appreciated!!

My cycles have always been always irregular. My cylcle started 5/11. I got a positive opk on 6/3 which is CD24 of a 32-35 day cycle. I got a very faint positive on 6/13 -CD10. On 6/14 two lines were very visible. The lines have been darker each day I take them. Yesterday afternoon was almost a dye stealer. I expect to be around 4 weeks and 6 days to 5 weeks pregnant. According to my last cycle I would be 6 weeks and 2 days. I went to the OB yesterday they did an transvaginal ultrasound but wasn't able to see anything.No gestational sac was visible. My OB did blood work to test HCG, and said depending on what comes back. It could be pregnancy, ectopic, or miscarriage. My HCG level yesterday was 728 and progesterone was 16.1. Is it really to early for ultrasound to detect or should I prepare myself for the worst??