Gained some and then lost it plus more...

So I started off this pregnancy overweight so I'm aware I don't need to gain much. 
However, up until 12 weeks I didn't gain anything and then from 12-16 I suddenly gained 5 pounds. 
Well, now at 26 weeks I've lost that 5 pounds plus and additional 7. Making me 7 pounds down from my pre pregnancy. 
Should I be concerned that I am losing? Baby appears to be healthy and my doc hasn't said anything but I just want to be sure