Overheating

My 2001 PT crusier has been overheating. I changed the thermostat and a hoes. Now it's overheating when I get off the freeway. I drove it with the defrost on and it ain't overheating.

You may have air in the cooling system, needs to be purged out by running the motor to operating temp. with the radiator cap off, the heater set on hot, and keep refilling as necessary until full. Coolant may come out the radiator, but that is just the air working threw. Put the cap back on when done and the engine running before turning off the motor.

I had that done yesterday and it did fine for an hour

How about the fans on the radiator? Are they working?

I don't know how do I check that

When the engine is to operating temperature at some point the fans should kick in to cool down the radiator. So open the hood and just watch, but don't be letting it over heat. That is not good on the heads, they can and will warp.