Non-refundable ticket changes will cost you. As of 2013, Delta charges $150 for changes to domestic tickets and $250 for international tickets. If you booked your Delta flight through a travel agent or an online agency, you will be charged an additional $50 to make any changes to your ticket.
In the U.S., approximately 3.3 million people have OCD, of which you have 0.3 to 1% of pediatric population and 2% of adult population. So about 1 out of 200 adults have OCD and twice as many have had OCD at 1 point or another in their life.
OCD is a common disorder that affects adults, adolescents, and children all over the world. Most people are diagnosed by about age 19, typically with an earlier age of onset in boys than in girls, but onset after age 35 does happen. For statistics on OCD in adults, please see the NIMH Obsessive Compulsive Disorder Among Adults webpage.