I caught my son wasting lotion that I told him he had to use after his shower?

Sounds like he's resentful about using the lotion and your nagging him. At this point, he's 13, not 8, so you should tell him you know he was wasting it, but that you're not going to do anything, because he's old enough to know what is best for himself. So you won't mention it again, but you'll leave lotion there for him to use if he wants it. It's his decision, and he will suffer the consequences if he doesn't use it, and reap the benefits if he does.