Hi CoastalGurl, and welcome to the forum.
I had something similar, I had been without periods for 14 months, and had been using local oestrogen for bladder issues for approx 6 months, I had a light bleed. So contacted my GP and she referred me straight away for a hysteroscopy, I too convinced myself I had cancer!
But hysteroscopy showed lining was actually quite thin and no concerns, but to enable me to use oestrogen, the gynaecologist recommended the Mirena coil which I now have, and use oestrogel 2 pumps daily, and all fine.
How long were you on the Everoel conti? I'm surprised your doctor advised coming off it so soon, I'm no doctor, but from the advise I've read and been given in here, most HRT regimes need at least a 3 month trial for your body to get used to it.
Chances are, the oestrogen in your HRT may have caused a light bleed, I spotted for at least 6 weeks after having the Mirena fitted and starting the oestrogel.
No doubt other more experienced ladies will be along to offer advice, but I would say try not to worry, it's probably the disruption from the HRT starting it then stopping it so soon.
Internal ultrasound isnt painful, hysteroscopy was uncomfortable, but taking ibuprofen before you go will help xx