Unusually sore after exercise ?

I'm 16 weeks pregnant and I'm sore for DAYS after a workout. I don't do anything crazy. I workout 3-4 days a week. Will ride the bike and lift weights (way lower weight than what I did before pregnancy). I never over due it or get my heart rate too high. I mean I used to work out hard core before pregnancy so I'm not doing anything new at all! Why am I so darn sore? I mean hell I went on just a 4 mile walk Saturday, no jogging or running and my legs still hurt when I sit on the toilet? lol is this normal?