I agree with gymdandee. Schedule an appointment with your doctor. Try to remember when this symptom first appeared. Also take note of any other symptoms you have been having, even if you don't think that they are related. There are many conditions that can cause aching joints. Another important piece of information that your doctor will need to know is where are the pains, how long they last, what time of day, and what type of pain (burning, aches, stabbing, throbbing, bilateral-both sides at the same time, etc.). Listing other symptoms may help to determine what they need to be looking for. Sometimes symptoms are subtle and and you may not think they are connected, but tell the doctor anyway. Best of luck!
It could be any number of things including Fibromyalgia and costochondritis
I suggest seeing your doctor and checking it