6 week ultrasound showed empty uterus

Wondering if anyone has any similar experiences good and bad they could share? I'm 39 and had a miscarriage in April this year and I'm roughly 6 weeks 3 days now. I had a weird gush of blood last Tuesday as a random incident and just occassional brownish spotting since. No cramps. I had a scan last Thursday after bloods and although my levels are rising (but not doubling) there was no sac seen in my uterus! The lady said she saw a place were something might be happening but my doctor says they should've at least seen a sac. Given I track my cycles, used Opks and temp I'm pretty sure my dates are right. The doctor says I'm either very early and my dates are wrong, I'm having an ectopic pregnancy or possibly a miscarriage? She's suggested waiting til next week to have another scan but she was hoping I'm just really early. So my question is has anyone been through similar, trying to stay positive but it's hard atm... thanks in advance!