Calf pain after exercise is usually from one of two causes: vascular claudication or neurogenic claudication.
In vascular claudication, there is not enough blood getting to the calf muscles, thus they begin to hurt and even cramp. In neurogenic claudication there is stenosis of the lower spine, causing pressure on the nerves to the legs, causing pain.
The way doctors usually differentiate the two is by history first. If you say that you get the pain and you have to stop, standing, for awhile, then you can continue - it's vascular. If you get the pain, and have to sit down or bend over with your hands on the knees - it's neurogenic. Now, that's just the start, to help direct the doctor in what tests to get first.
For vascular problems, a doppler-ultrasound of the legs is usually obtained. Then, if needed, a vascular surgery consult.
For neurogenic claudication, an x-ray and MRI of the spine are usually obtained, followed by an orthopedic spine or neurosurgical spine consult.
Both conditions can occur at the same time, of course, but it's usually one or the other. If it is not one of these two, then the doctor will have to do some deeper digging.