Why does my left testicle go up into me?

I am a 15 year old boy who admittedly masturbates once or twice a week. And I just noticed right before I was going to , my ball was missing! But it wasnt missing it was just up parallel to my . So can someone please tell me why this is just one testicle and why I just noticed that happened? Thanks. And P.S I do not have ann undescended testee or testicular cancer.