Hi Beverley - you are most likely bleeding because your womb lining has thickened (termed oestrogen breakthrough bleeding) - this should have been explained to you after your scan. The tests are clear - meaning there are no abnormailites (eg fibroids etc, no hyperplasia, cancer etc) but a thickened lining can lead to endometrial hyperplasia which can lead to cancer if unchecked. The fact that it has thickened is either because you are still peri-menopausal (even though taking continuous combined HRT) - but this is unlikely if you haven't had a bleed for 5 years, or because the balance of oestrogen to progestogen in this particular HRT type is not right for you - specifically that there is insufficient progestogen to keep your lining thin.
I would suggest the doc is wrong to say nothing to worry about - as s/he should understand the risks of the womb lining continuing to thicken, untreated - of which the bleeding is a good early warning sign!
If you feel otherwise well then a course of extra norethisterone should allow a bleed so enable the lining to be shed, or else a higher dose generally. The other alternative is to take separate oestrogen and progestogen - so an oestrogen tablet (2 mg as you are taking) with norethisterone at a higher dose - but this is not usually prescribed separately as part of HRT though no reason why not. As the HRT you are taking contains 1 mg norethisterone you would need a slightly higher dose to keep your lining thin - if you are otherwise OK with this type. Another alternative is an oestrogen tablet with Provera, a different type of progestogen - which can be taken at lower or higher dose - whicever is needed to keep the lining thin.
Finally another alternative is the Mirena coil which is very effective at preventing the womb lining thickening and limiting bleeds. I am suprrsed the doc did not suggest this to you?
Do have a think about these options and then go back to your doc. You shouldn;t have to put up with abnormal bleeding! If your doc isnot knowledgeable then find another in the practice who is...
Good luck and let us know!
Hurdity x