Master baths are often distant from the rest of the plumbing in the house, so they often have their own plumbing vents independent of the home's other plumbing. If the flushing performance is anemic and there are no clogs or obvious malfunctions, there may be an amazingly simple remedy. Occasionally, plumbers forget to remove the temporary plug that's used to pressure-test the lines after plumbing rough-in. They're located at the top of the vent pipe up on the roof. If you can't see a rubber cap clamped on the vent over the bathroom from the ground, climb up on the roof and inspect the end of the vent over your bathroom and I'll bet you'll find an overlooked plug. If so, break through the plastic with a screwdriver and pry out the pieces and that toilet will work just fine.
If that isn't the problem, you probably have a defective toilet or an obstruction in the drain line. Get ahold of the plumber who worked on the house. He or she should be able to solve the problem.