I've been playing bass for two years now. The first 18 months of playing, my practice sessions were really productive and I've learnt a lot in those months. The last six months have been awful. I have learnt about five new songs and whenever I wanted to learn new songs, I put away my books after about two minutes. My practice sessions have consisted only of playing the same songs I have been playing for over six months. I am now tired of those songs, and I can't stay concentrated when I'm trying to learn something new. This has led to days on which I don't take up my bass at all and on the days that I do take up my bass, the practice sessions keep getting shorter. What can I do to be able to concentrate on learning new things and enjoy practice again?