Any rapid increase in physical activity is bound to make you feel weaker. Especially in two sports which require a lot of leg movement which is hard on your knee's
I would say its just from working so much but I'd keep an eye on it. If you can, try and take a break every once in a while. If nothing changes, see a doctor.
I have a friend who was a club soccer player and can no longer play because she has CRPS which is complex regional pain syndrom. Only, her pain is unbearable and she cannot walk without crutches.