Inner Tube - Cosmo 2.0/ Cosmo 2.0 T

I love the bike itself. After a little over a year of riding I got my first flat. It took me 4-5 hours trying to change the innertube and put everything back on. The innertube only lasted a couple weeks and it’s flat again. It was in my garage for a few days and it went flat for no reason. It won’t even pump up anymore. I’m not sure what’s wrong with it but now I have to spend 4-5 hours to change it again.