What could cause my intense fear of needles (shots)?

What's excessive?: Nobody likes shots. Phobias grow as avoidance of the feared event increases. Perhaps your fears have caused you to exaggerate the pain associated with shots. The fears can go away quickly. I treated a person with shot phobias who shortly after starting treatment was dx'd with diabetes. He had to start giving himself Insulin shots and lost his shot phobia in about one week. Quick cure!

CBT: Seek a cognitive-behavioral therapist who specializes in phobias. One method they use is systematic desensitization which slowly and incrementally brings the person closer and closer to the thing they are afraid of in slow, graduated steps that help make the anxiety more tolerable.