Normal or a bad sign?

I’m 28 weeks pregnant today and I’ve been noticing for a few weeks that if I stand up for more than 10 mins or so, my heart starts pounding really fast and I get really hot and sweaty. I’ve also noticed my pulse beating harder (even just sitting down) since about a month or so ago. Brisk walking doesn’t bother me though.. Could this be a bad sign or is it just a normal pregnancy symptom?