I would personally stick to the routine you are doing, however level it up bit by bit. Example: you are doing an easy workout and you can’t feel as much as you would like, you would then level up and extend that workout. Add more exercises, more harder ones. Eventually as you try your best, the hard work pays off and staying and eating healthy benefits dramatically to fitness; energy, nutrition for growing etc.
Try new types of exercises that activate different muscles. If you are usually into aerobics, keep aside a day for pilates, or weight lifting, or simply skipping ropes. Make it fun by adding zumba or just dancing to your favourite jazz to the routine! You may be surprised to find many yoga forms that could be seriously challenging to you! There are so many fun workouts out there, try new exercises with new music to have fun while enjoying the burn:)
It’s important to have variety in your exercise to not have it go stale. Do leg day one day and do arm day another day for example. If you aren’t getting sore anymore, amp up the difficulty!