Serpentine belt squeal

So my belt is squealing. I brought my car to the shop because before this squeal it sounded like a rattle and I thought it was a bad timing chain but it turned out to be a pulley. So I had the mechanic repair the pulley. He said my alternator was bad also. But I just had my alternator replaced not even a week prior and it was replaced 2 separate times before that in only 4 months. And also about 2 months ago I had a new belt and tensioner put on the car. So that's a brand new pulley, tensioner, alternator and the serpentine belt itself. Anyways, I get the car back from the mechanic and the rattling noise from before is gone, but now the belt is squeaking badly. And all my warning lights on my dash are turning on then off and on and off again and again as I drive. Sometimes the belt stops squealing after it has warmed up and sometimes it squeals forever. What is the problem and how do I fix this annoying ass noise? I already spent way more than I bought the car for and definitely more than the car is even worth in repairs. And it's still having problems and I'm getting very frustrated. Please help me.