I'm curious as to how the subject of cancer came up with your doctor. Did you ask him/her if aches and pains could be a sign of cancer? Did he/she bring it up themselves?
If you are having consistently achey, painful symptoms, your doctor should order a complete blood count (cbc) to test for rheumatoid arthritis, lupus, thyroid, etc. If all tests are negative, then I would ask for a referral to a rheumatologist so you can be evaluated for fibromyalgia and other arthritic-like conditions. A general internist cannot usually do this type of an evaluation (that is, beyond the blood-work), as it is a specialty of rheumatology.