2007 Cadillac CTS

Hi All: I have a 2007 Cadillac CTS I bought used last March. In May 2014 I had to replace the battery. In Oct 2014 I had to replace the alternator and the battery again. Two weeks ago I had to replace the starter. The car will not start without a jump and once you turn it off it does not start again without a jump. I had the battery tested at autozone and they said the battery is fine. The car also does weird things. The radio will turn up out of no where, the back drivers side brake light keeps blowing, the sun roof opens when it wants to. The cigarette lighter works sometimes then not other times. Please help I’m at a total loss.