confused about weight gain?!

I am 5'5" and prepregnancy I was 145 lbs. I've done research with my first and second pregnancy and everywhere I have read saud that normal weight gain for my height and weight would be 25 to 35 (which sounds normal to me). My doctor for my first pregnancy wanted me to keep my weight gain. to 35 lbs and I gained 40 lbs and was able to lose it all after baby was born. I talked to my doctor yesterday (I'm 17 weeks) and she said for my height and weight to only gain 15 to 25 lbs. I'm so confused. I'm not heavy set at all, I have some extra weight on me but that's normal. I just think 15 lbs is not enough to gain. My first baby was 7 lbs plus all the fluids, placenta, etc. that comes out with baby, I lost 20 lbs right after birth. what do you ladies think?