Why is my car overheating & why is coolant revisor boiling?

Overheating and boiling in the reservoir are the same thing basically. Do you have a coolant leak? Maybe it's a stuck closed thermostat, faulty water pump, or a head gasket issue. Further testing is required.

Yeah, that's not usually good, but sometimes it can be something more simple than a head gasket. All I can say is, if the car is in good shape otherwise, and you like it, IMHO it's worth fixing if you can swing it. They are one of the best cars ever made reliability wise, and if it isn't worth saving, an early 2000's 4 cyl Camry that was treated right is even a better engine due to the timing chain, not a belt like your 99. I hope you get it straightened out and more importantly, report back here what the fix or result was so it helps others. Good luck!