the Queen's Gambit is a gambit specifically because black can hold on to the pawn for the time being. Your goal should be to build a good position and recover the pawn along the way, not being hellbent in getting back your pawn asap.
4.Nc3 is the most natural continuation.
It prevents black from supporting with b5, and controls d5 and e4. Right now we're threatening to advance with d5. The following plans can include attacking the e6 bishop with either Nf3-Ng5 or Nge2-Nf4.
If black plays c6 to prepare to support the pawn even more then he's taking away the best square for his knight. If you want you can play a4 to prevent him from playing b5.
I like running Queen's Gambit and love it even better when it is accepted, however I've come across an where black queen's bishop protects c4 pawn. 1. d4 d5 / 2. c4 dxc4 / 3. e3 be6?!. I'm not sure what to do after this to regain the lost pawn.
Any help what be nice.