My elbow hurts every time I throw a ball?

It depends. In a younger person, this could little league elbow and break down of the elbow joint that can lead to long term elbow problems. If the pain is medial and goes into your ring and little finger, it's probably cubital tunnel syndrome, which is a pinched nerve on the inside of the elbow. If its the outside of the elbow, it may be tennis elbow syndrome. If it keeps hurting see a doctor.
Elbow pain. Most common causes of elbow pain include tendon (medial and lateral epicondylitis), loose bodies in the joint, irritation of the ulnar nerve, or sometimes a small piece is synovium may be getting pinched. Consult with an upper extremity specialist for an evaluation.