Is it fatigue, eyestrain or dry eye syndrome that makes my eyes feel funny when working on computer for 14 hours per day?

Fatigue. Although each of the causes you provide are possible, i would suspect fatigue and address this first by resting with eyes closed for five minutes every hour.
All of the above. All of those issues are involved in this issue. Take breaks periodically and use artificial tears to lubricate your eyes to avoid these issues.