You mention that you typically work out in the evenings -- this has been something I progressively came into doing myself, and I wonder if it hasn't been the cause of my plateau/slow 5-10 lb regain.
I know so many people would balk at the idea of doing this, but would it be possible for you to do a cardio session (like running or biking) before you eat breakfast? Because you mention that you've already lost 45 pounds doing your gym routine, your body has probably become accustomed to the routine, and no longer uses as many calories doing it. I'm just changing the timing with my usual 1 hour/day cardio schedule, and although it's only been like 3 sessions so far, I do think it's helping. The other thing, too, is that you're likely just burning the calories you ate earlier in the day when you workout in the evenings, rather than your own body fat. This is the main reason why working out in the morning is so effective.
The other, possibly more palatable, suggestion is that you spend more time on cardio. Even with the kickboxing classes, 30 minutes 3-4 days a week will cease to be effective once you're in good shape, which it sounds like you are
So it's kind of a good thing, maybe, to be plateau'ing: it means your body must be more fit and efficient!
Plateau :(
