Levels dissapearing

I started playing Minecraft as a kid and stopped playing for a while then recently have been playing a world with my boyfriend. I've never encountered this problem before. The problem is that when I'm playing I will gain levels, and they either won't absorb orbs or my levels will drop from 23 to 18 to 16. It isn't happening to my boyfriend who is playing on a console, but I am playing on my Windows computer. We don't have anything special added on, it's just plain simple Minecraft. It started to happen after the new update so I don't know if maybe that is it. Or if it is my computer being funny.