It could be one out of a hundred reasons, or a combination of some or all of them. If you have stomach pain, and it persists, see a physician (especially if it is a stabbing type of pain).
I would suspect an ulcer.
Possibly an ulcer, or maybe acid reflux...
Muscle strain. Often caused by exertion such as lifting weights. Possibly from whiplash.
Coughing and Back Pain
Heel Spur Syndrome
How to Determine Middle Back Pain Causes
Pain Caused by Cervical Spine Fusion