Symptoms such as you describe could be coming from the neck, shoulder, elbow, or wrist. Pressure on a nerve anywhere along that course could cause the sensory changes you notice as a cold sensation. Likewise, a change in pitching speed or accuracy could reflect motor nerve compression or impingement.
Chronic repetitive motion and especially the overload from pitching with force can slowly cause soft tissue degeneration around the elbow. Age is always a factor as the aging process combines with the chronic mechanical forces to create microtrauma that eventually catches up with us.
You didn’t mention any pain, numbness, or tingling or say anything about popping sensations. Additional symptoms like these can give clues to the underlying problem. A visit to an orthopedic surgeon or sports physician may be a good idea. A complete history and examination will most likely reveal an accurate diagnosis, which would lead to the appropriate treatment.
A simple X-ray may be all that is needed to reveal bone spurs, tumor, infection, or arthritic changes. More advanced imaging isn’t usually necessary but if needed, MRIs and CT scans both offer helpful images to determine the cause of the symptoms.
Of course, treatment will depend on the diagnosis. Many elbow problems such as you described can be managed nonoperatively. A carefully prescribed rehabilitation process can get you back into full sports participation again. Newer treatment involving blood injection therapy (called platelet-rich plasma) to help speed up healing may be a possibility as well.
But before jumping ahead to the actual treatment, get a medical examination and find out what’s wrong first. That’s likely your next best step.