In the pg books I have read it seems the weight gain should come on moslty toward the end of your pregnancy, and that an early weight gain is a sign of overeating.
Who knows.
If you start out "overweight", a typical pg weight gain is bet 15-20 lbs and if you start out "obese" it should only be betw 6-15 pounds.
145 does not sound overweight nor obese to me...but maybe you are simply eating so correctly that your baby is making good use of the food you take in?
I am having weight issues myself...I am just about to post about it!