pressure check for a blown head gasket/intake gasket. cheeck coolant level first.

Coolant level is low it has went low everytime i filled it. Ran rough lots if blueish smoke..I turned truck off now Truck will not turn over at all. Starter only 3 weeks old. Could motor be seized up? Will the entire motor need to be replaced or just the head?

pull the plugs out and see if it will turn over. if to much water got into a cylinder you probably hydrauliced it meaning you bent a rod because piston was trying to compress water. doesn't do that very well at all. if that is the case then it will be rebuild current engien or replace it. you really will have to tear it apart to find out damage now. but try the plug removal and see if iturns over, if it does then it's probably a top end problem like do the head gasket resurface heads, etc.

Remove all plugs or just one of them? When I tried to turn it over there was a loud thunk and it won't turn over at all now

that sounds like a rod that hydrauliced or a bolt on torque converter came loose but i'd go for the rod. you'll find out when you pull the pan if you choose to do so. you remove all the plugs.