Get out of your comfort zone. 
As you know, that old saying goes 'The definition of insanity is to do the same thing repeatedly and expect a different result'.
That is absolutely true when it comes to exercise! If you do the same classes, lift the same weights, run the same route at the same pace, your body will adapt and learn to store energy rather than expend it on the brainpower and physical strength and stamina needed to tackle new tasks.
You don't have to give up what you do now - just incorporate change in bits and pieces. Start by trying a do-it-yourself circuit. Set your phone timer to 10 minutes - grab whatever you have available (hand weights, skipping rope, step) and just keep moving until the timer goes off. Aim to get sweaty! If you want some ideas, ask a trainer, look through fitness mags or watch what other people are doing. Just make sure you do it safely! Being in the eyesight of a good trainer is a good idea for this one.
Doing it differently is how you make yourself stronger. Don't wait for tomorrow.