Typically I can tell me e2 is low due to anxiety/numbed mood, then comes the joint pain. I noticed that when my e2 is low, I don't look dry like others would suggest due to lowered water retention, rather I seem to have a real flat looking tone to my muscles as if I won't hold glycogen well regardless of my diet (which keeps my looking full normally), this also comes with lowered strength/power and a reduced pump. AFAIK the reason for this I believe is estrogen is important in either glycogen uptake or synthesis or insulin sensitivity in muscle (something like that anyway).
Also, how much exemstane are you taking and what is your current TRT protocol? I assume it is liquid stane not tabs?