Are we talking "flashes" here? Yes, it's a symptom of nolva, but also of elevated estradiol.
I would up your aromasin to 25mg ED for the first week, then 12.5mg from second week on. I usually recommend 25mg for the first week of PCT, and UGLs are usually underdosed with aromasin. Good choice with aromasin/nolva.
You could also be pregnant, but I know better than to ask.