It depends on what causing it. the only thing I can say is to drink plenty of fluids but I would recommend to go see a doctor, if you are unsure or worried.
Answer:
some stuff to consider when designing a cross training routine-
your goals
balancing your routine
inclusion of activities into routine
activities that can be used in daily routines
Explanation:
Known as cumulative trauma disorders
I do believe it's all of the above. Although, it might not be trouble sleeping. That might be true in some cases, but not in all.
Go running
go swimming
working your muscles and ligments