losing weight while pregnant

just curious if it's different for everyone. I'm overweight and pregnant with our 2nd child. My trainer said that I could still lose weight while pregnant and focus on my strength training (nothing hardcore just maintaining what I could already lift) well I asked my obgyn about it , but he said no I can't lose weight while pregnant and couldn't lift more than 20 pounds.. my friends obgyn told her friend that yes she needed to lose weight because she was also big during her pregnancy. so just curious on what everyone has been told. I'm not looking to lose alot of weight. just really want to neat right again and exercise , and not gain alot with this one. I'm still packing on the 40 pounds from the 1st one -_-