No pregnancy picked up on scan??

Rebecca • Beautiful baby girl born 12th September 2018 - love my little family 👨‍👩‍👧🐶

So I went for an ultrasound today for an issue I've been having for about 4 months, lucky me I had a positive pregnancy test on Xmas <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a>! my Dr told me to still go to the scan after predicting I'm about 5 weeks pregnant, but I had an external and internal scan and they couldn't pick up on a pregnancy... I'm being referred to the early pregnancy centre for another scan 2nd or 3rd of Jan. has anyone else had This? what was it? I don't think miscarriage as I believe my hcg levels are still rising (on home pregnancy tests) every other day, I've had NO spotting, not even a little Bit, mild cramps very occasionally so nothing to worry about. can anyone share their experience? The hospital today said might be too early, but they did also mention ectopic pregnancy...... any help would be appreciated!!!