Battery keeps dying and nothing on the dash works

I started my truck and the everything was fine until I started driving then the inside lights went off and came back on then the outside lights did the same while I was driving. I figured it was the battery so I bought a new one. The next day my truck was dead. I got a jump and it started but the same problems occurred this time nothing on the dashboard worked. (Speedometer, gas light, etc.) Then the battery light came on. I changed my alternator this time last year so I didn’t think that was the problem. Someone checked my truck and said I had a loose belt and the tensioner pulley was bad. So I changed that and charged my battery and my truck worked for the first half of the day then the security lock came on and wouldn’t let my truck do anything. My sisters boyfriend unhooked the battery and it started but the lights on the outside wouldn’t come on. I turned it off and back on then the outside lights came on and the inside didn’t (same problem). I made it home but the battery light came on while I was driving. I got my fuses checked and the problem is still there. Someone said it sounds like a shortage or something simple but the problem is finding out where the shortage is or if that’s even the problem. I don’t want to spend anymore money on parts until I know what’s the problem. Think you can help?