JoannFran the honest answer is it has taken me two years of self education, blood tests, research and trial and error to be able to understand what was going on with me. It is not a clear cut case (maybe Peri never is!) especially as I'm only 42. (I do love being able to write "only" 42 every now and then
![Grin ;D](https://www.menopausematters.co.uk/forum/Smileys/extended/grin.gif)
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Everyone is different but for me blood tests have been vital to understand what is happening, however without a benchmark to go on, it can be tricky to interpret ("is this lower than it was before?")
If it were me, I would be getting a blood test on day 21 of my cycle and seeing if that sheds any light. If your E is below 350 that's a good marker for needing HRT however as many others will point out, your E level is not always a diagnostic factor.
What actually happened with me was that in early Peri my Estrogen soared for about 2-3 years (late 30s) during the luteal phase day 14-28. I know this because I was having terrible painful boobs every month and it triggered me to get a blood test which showed my E was way above the top of the range. No one told me it could be Peri, I didn't have a clue, and I did nothing about it. Fast forward two years and my E then started to fall back down in the next stage of Peri and it was this fall from very high even down to middle that caused me to be highly symptomatic. It is known among decent meno specialists that your E doesn't even have to be clinically low for you to be symptomatic (which is why many doctors rightfully diagnose on symptoms alone) and it can be the fall from "very high" in early Peri down to "middle" which triggers symptoms. Once I started HRT my problems disappeared (except for a few hiccups along the way).
This is a long winded way of saying I don't think there is a one-size-fits-all, but it is absolutely possible from my story alone that your situation could well be estrogen deficiency despite only experiencing it for half of your cycle, however as you say it could also be low Progesterone as that falls first in Peri.
Another option other than a blood test is to do a Rhythm hormone profile test from Genova Diagnostics. I've done 3 over the years and found them very insightful. They are salvia tests but you do them every other day and they chart your hormone levels (both E and P) for you, so you can see what's going on over the course of the month - they aren't cheap but I have found them super helpful to correlate symptoms with a change in levels.
Hope any of this waffle helps xx