2002 Pontiac Grand Prix Weird electrical problem and car wo

I have a weird electrical problem that started a couple a months ago it started with just little thing like the radio would turn off and come back on. A couple weeks later it would have trouble starting the engine would turn but wouldnt start I had to give alot of gas for it to start and I would have to rev it up for a little bit if not it would stall. A couple days later I had problems with the alarm on the car it would go off while I was driving or when I turned the car off. Now the car wont start at all I turn the key nothing happens and my door locks dont work lights and everything but my battery is fully charged and lights in the dash flicker and if I turn the key back on accessory radio and lights will turn on so I just keep trying and trying and after a while it will start and everything is fine for a few days and problem will come back again?