Are you still taking your prenatals? If so, talk to your doctor about adding iron. When I told my doctor I was getting exhausted, especially after baby did her daily aerobics, he put me back on my prenatals (I had stopped taking them because I was so sick and the size of the pills would activate my gag reflex so i couldn't keep them down) and told me to add iron. Since I've been back on them I'm not nearly as worn out.
Sadly, yes, I'm on my prenatals and iron!