I don't understand, they told you to stop HRT because of a discharge which they couldn't diagnose or treat - and you're just supposed to stay off HRT because of it forevermore?? What about your menopausal symptoms....? I wouldn't accept that
Estrogen can increase vaginal discharge, because it lubricates the vagina, makes it moist again and returns the ph to the slightly acidic Ph it should be. And yellow-ish discharge can be normal, for some women. I guess it depends whether you remember having it before, earlier in your life when you might have had more discharge?
Why is it stopping you from having sex, does it hurt or do you have other irritation or symptoms? Does it smell? Does it smell really acidic, like vinegar?
There are also different types of vaginitis. I've been reading up on this because I think I might have something like it. If you've been tested for thrush and BV and those tests are negative (as mine are), then it could be vaginitis - just from an overgrowth of normal bacteria for eg:
https://www.webmd.com/women/cytolytic-vaginosis Doctors can be a bit useless when it comes to diagnosing these more obscure things. I'd go back to your doctor and ask to re-start the HRT as there's no reason to stop it just because of some discharge they can't even diagnose. You could try the baking soda tip in the article above - I think the easiest is to get some vaginal syringe applicators and put the recommended douche in there and just use it in the shower. You could also try using some YES VM vaginal moisturiser 2x daily with the internal applicators - this is the right ph for the vagina and could help rebalance it. (Someone elsewhere recommended using Preseed vaginal lube and found that fixed it for them - but it has parabens in it, so no ways that's going up me!)
PS there are also other vaginitis-es - like DIV - desquamative something vaginitis - so do see the doctor again if the stuff you try doesn't help. If they appear to have no idea, ask for a referral to gynaecology.