I guess this begs the question - what does your 'typical workout' entail?
If you're already doing weights, mix it up. For example, if you are doing 3 sets of 15 reps of weight, add a couple of plates and try 3 sets of 8 reps. It's a common misconception that women 'bulk up'. Most that do are usually supplementing, using an estrogen blocker or testosterone enhancer, all to get the heavier physique.
Mixing up your weight training can be as easy as changing your sets and reps, doing a different exercise for each bodypart, or even doing the exercises in a different order. Shocking your muscles creates growth, and muscle growth enhances lean body mass, burns more fat, and can even give the 'illusion' of 5 lost lbs in very few workouts.
As to your cardio mix, if you're doing 30 minutes, extend it to as much as 60 minutes for a greater fat burn.
It's all about confusion - muscle confusion, that is! When your muscles do the same workout, day in and day out, you will get gains - but not as much as when your muscles have to do more work, or different work!
Another quick and easy mix is, if you're working out 3 times a week with a standard cardio warmup, followed by weights, followed by a major cardio workout, try this: Extend your workout, temporarily, to 5 days a week, and do every other day weights and every other day cardio. One day strictly weights, one day strictly cardio, etc. etc.
This should help jump start your training in a whole new direction! (...and don't say 'just three weeks'. That's a whole lot of time to lose 5 lbs, or tone up the weight you have!)
Good luck!