My alternator went out on my car so I had to replace it but my car is

I had to replace my alternator in my car but once I did I noticed that I had a service theft system light and shortly after I had a charging system failure light and a battery light .

I know my new alternator is good I e had it yesterday from the auto parts store I purchased it at.

I know my battery is good because I just purchased that as well I don't know why my car continues to die on me and is acting like it had a bad alternator when it's good .

And these lights I was telling you about come and go as they please one minute they won't be on and my car will be normal and act fine the next minute they're on our nowhere and my car is loosing power