Early Ultrasound

I began spotting yesterday, brown discharge, with some mild cramping and a little burning here and there, fast forward to today and an OB on call got me in for an ultrasound before work, I’m measuring 5 weeks and 1 day, they could only see the gestational sac and nothing else, my doctor says everything looks fine and he wants me to come back for another exam this Friday and probably another ultrasound next week. My hcg levels seem to be rising normally, I’m at 3218 as of yesterday. Anyone have anything similar? Outcome? Was my ultrasound just to early to see anything? Just wish this wasn’t such a slow process