You may have a problem with coolant (antifreeze) making its way into your combustion chambers. This is commonly referred to as a 'blown head gasket'. If so you're looking at a large repair. There are several tests a good shop can perform to determine this for sure. It would be a good investment to have a competent shop find out for you.
I agree with integrity first automotive. However, this problem could also occur if the intake manifold gasket has failed, even if it is new. Finding out what the problem is should be inexpensive, and then you can decide which way to proceed with fixing it. A WORD OF CAUTION: if there is white smoke coming from the tailpipe, do not drive the vehicle, as more damage could be done, and the cost of repair will be much higher.