suggestions for my weight gain

Mommy
Help! Wasn't overweight to start but was on the higher end of the normal range for my height and frame. I'm 15 wks and have gained 8 lbs so far. Hoping not to gain more than 25-30lbs total (realistically.) that means only 20 more lbs in 24 more weeks. A) is this possible? B) how can I make that happen? 
I gained 50 lbs total with my older children. Way too much. I was also really small prepregnancy to my older ones. Over a decade ago. Tips and suggestions please. I already drink lots of water, do the elliptical and don't really eat junk.
I think the issue is I was only eating 1200/cals per day prepregnancy and due to nausea couldn't eat much first few weeks. So now I've jumped up to 1800 cals per day and it's packing on some weight