07' Sierra 1500 classic wont start after running

[Nickvvv]

So it started happening to me about a week ago, my truck would just randomly not start. When it first happened, it would struggle to turn over. I said no problem and just bought a new battery for it. About 3 days after that, I went to the store and was only in there for about 2 minutes and got back in my truck and out of nowhere, nothing happened, not even a click. I checked my connections as best as I could, and eventually had to get jumped. Tried it again as soon as i got home, turned it off, immediately tried to turn it on and once again, not even my dash lights were coming up. I jumped it and took my negative off to see if it were the alternator or not but it kept running. Any thoughts?