Different Pregnancy's = Different Symptoms?

I am pregnant with my second child, my first is 5 years old and will be 6 by the time I deliver. With him, I was THE worlds happiest pregnant lady. Zero symptoms ( except having to pee every 10 min!). With this pregnancy, I have been so sick, tired, sore boobs, etc. I have been a horrible miserable person the last 1 1/2 months and I am so exhausted already! Has anyone else experiances differences like this with different pregnancies? I have not yet had my ultrasound, but I am starting to wonder if there are twins in there!