When your body is used to the same movements and resistance (exercises and weights) that you're doing, it stops working so hard and you're really just wasting your efforts.
So, here's an idea.
Ask a friend or a trainer what their exercise or gym routine of choice is and commit to doing it - maybe just once, maybe a few times! Perhaps you'll find you LOVE bikram yoga. Maybe you'll go orienteering instead of doing the same Saturday BodyPump you always do...
Who's going to do Fitness Swap? I dare you.