Doctors use "aches and pain" on a regular basis, even in medical literature.
According to my doctor, patients gwenerally refer to anything dull as an ache, and anything sharp as a pain.
My doctor, at least, defines an ache as a pain not caused by an injury, or a specific damaged area due to disease, such as a heart attack.
He defines a pain as an injury that needs treatment.
Both can be sharp, but an ache is a overall, general problem, as with sore muscles. A pain is a torn muscle that needs repaired.
An ache what you get in your lower back from setting in the same, poor position for too long. A pain is when you have a crushed disk in your lower bck, and the pain doesn't go away when you change position.
An ache if when you finger hurts from pushing buttons all day. A pain is when your finger gets chopped off.
In other words, an ache just happen because of circumstance, and goes away on its own. A pain is caused by damage, and requires medical attention.