No gestational sac?

So yesterday i went in at 5w2days and it was just for pain i was having. The on call doctor told me he sucked at transvaginal ultrasounds but wanted to do one to just check. He didn’t see a gestational sac or anything on the ultrasound he did but my hcg level was 1677 yesterday. I go in tomorrow to make sure my levels are rising correctly, but has anyone else been through this and it turn out ok? He said he may not see anything cuz he isn’t good at ultrasound and the machine was old but I’m just worried cuz i thought you could see a sac at least after hcg levels were over 1000...