Will not start

Hi, I will try to make this as clear as possible but if you have any questions, please ask me.So a couple days ago I was driving home from work on the interstate when I hear what sounded like something fly up from the road (or maybe from my car) into or out of the front end of my car. After that the battery light turned on. It was late at night so I continued to drive it home. The next day I went to AutoZone to have some tests ran and they said the battery is completely fine as well as the alternator. The only thing they could find was a bad o2 sensor and they said that was not much to worry about. So I continued to drive my car for a couple of more days. Last night as I was driving home from work the radio music shut off but the radio was still on. Then the brake service light came on. The radio then shut off as well and the airbag light came on. I was close to home so I kept driving. As I am on my street I notice the mph and rpm was fluctuating and said I was going twenty mph when I was going probably five. I tapped the brakes slightly and the rpm and mph both went down to zero even though I was still moving. Thankfully, I was right in front of my house. I pulled into the driveway and noticed my interior lights (I had already had them dimmed) were dimmed and would not turn back up as well as my headlights. I put my car in park and my engine was making a weird sound. I sat there for a couple minutes and then shut off my car. I tried turning it back on and it did not even turn over. All the dashboard lights turned on then off. I have had a couple people tell me this is my alternator. I am confused though because AutoZone said it was fine. What is your opinion? Is it my alternator? I have changed my starter twice in the past year, too. Thanks!