I have pain in my back, both sides of my spine just below my ribs, apart from tirdness and general aching, i have no other symptoms. what could it be?

Muscle aches: You are probably right, it is tiredness or muscle aches. However, physicians usually get a set of x-rays to make sure there are no problems with the spine. Remember that both kidneys are also included in that area. A physician may opt to working up the spine and your kidneys if need be.

Muscular strain: Myofascial pain try heat and massage, imaging not indicated.