No 1: you didnt specify what kind of car.

No 2: More than likely you have a loose ground. You prob hit a bump or normal vibration and it has come loose. Try to locate every ground and see if any wires are cut.

No 3: Depending on where u get your parts ( i only use Interstate batteries) your alternator might be sh*t. I've seen a lot of my buddies with hondas buy their own alt, and it still failed to stay funny. Make sure u didnt short your alt wire on the block anywhere.

-Ant.