Hi Kathleen, not an expert by any means
but that's right, though it's usually only considered to be oral oestrogen that can affect our requirement for thyroid replacement. The mechanism is that it raises Thyroid Binding Globulin, effectively making less thyroid hormone available for use in the body. So if you are on transdermal HRT perhaps that's why a TFT wasn't suggested. That said, some of us on here have found we need to adjust our thyroid replacement dose even with transdermal HRT. From memory it's been those, like me, who take T3 as well as T4. I've needed to increase my thyroid meds slightly when oestrogen dose has gone up & reduce it when taking less oestrogen.
Studies show progesterone also has (opposite) effects on thyroid hormone i.e. potentiating it slightly, but this is not generally taken into account.
Wx