99 grand am gt Overheating problems

I have an 99 grand am gt and it overheated on my wife going to work one morning. I let it sit for a couple of days and when I finally had a chance to check it out it was about 20 degrees outside. So I put about 1 1/2 gallons of antifreeze in it and bleed the system it was running for about 10-15 minutes and the temp gauge was already at 200 degrees. So I kept my i on the gauge and thats when I noticed the fans didn't kick on and that the heater was blowing cold air. about 5 mins later the temp gauge was going from 220 back under 200 and back to 220. So I knew i could drive it if it wasn't getting hotter than 220. I had to drive it about 15 miles home and the gauge went into the red and instantly pulled over and then the gauge started to go back to around the 200-220 mark. Why would the gauge be doing this and why isn't my heater blowing hot air? Could this be because my wifes friend put non dexcol antifreeze into it? The motor was replaced this past summer along with the tranny. the motor has about 100000 on it. I f anyone can help me with my problem i would br grateful. Thank you this is my first post on here.

Assuming a 3.1/3.4L? Prone to lower intake leaks which would explain the coolant loss. They are a pain in the ass to burp and will overheat if you don't get it right. Jack up the front end and let it run with the radiator cap off, see if that helps burp it out. You might have a thermostat/waterpump issue as well.