Whether you're getting night sweats or not doesn't really mean anything. There are many low estrogen symptoms besides night sweats, it's not really a reliable measure.
I would think it is your own hormones fluctuating underneath whatever the HRT is doing, which is causing it. That much is shown in your blood results varying from 200-something to 400-something. Although if you are on Yasmin, that's going to affect your blood tests and make them not reliable in terms of the estrogen results.
The best way to fix it is to actually take higher estrogen, not lower. That fixes fluctuations by buffering any lows. If you take less you might have greater fluctuations and when it cuts out, it will go lower.
I think it's more likely that you are progressing through peri, your own estrogen is fluctuating more and cutting out lower when it does, causing these symptoms.
Am I right you are on both Yasmin and also on HRT?? That's a bit unusual. I would think getting off Yasmin and fully onto HRT would be best and if you do need contraception, to take a POP or use the Mirena....