1998 Dodge Neon Loosing coolant and overheating

Bought the car used 6 months ago and no problems with it until Friday. Friday am going to work overheats. Pulled into a lube place and they told my girlfriend it was out of coolant. They filled it, and on her way, temperature fine. Didnt use it on the weekend, today, Wednesday, overheated, and I went and had to fill it up with coolant again. I got a full jug into it, between the rad cap and the reserve. Overfilled the reserve. Let it idle 10 minutes, went for a drive for 10 minutes, and then idled it for 10 minutes. No overheating, however the engine was smoking with burnt/evaporated antifreeze. The reserve was down to the max line. What do I need to replace? I've heard rad, hoses, thermostat, head gasket. All from various people with various knowledge.