Is what the questioner is experiencing—namely, delusions of intentionally breaking their fast in Ramadan, severe obsessive thoughts regarding ablution, prayer, and creed, and doubts that they have apostatized and their deeds have been nullified—an obsessive-compulsive disorder?

You are afflicted with waswasah (obsessive whispering), and its cure is to ignore it and pay no attention to it, whether it concerns wudu' (ablution), prayer, or fasting. Your fasting during Ramadan is valid, and you are not required to make up for it merely due to doubt. You must strive against yourself to cast off these waswasah, for Satan casts them into your heart to corrupt your life. Whenever Satan whispers to you that your prayer or fasting is invalid, tell him: "No, it is valid." The same applies to matters of creed; ignore its waswasah, for you remain upon Islam. Have a good opinion of Allah and trust in His mercy. If you do as we have advised you, by ignoring the waswasah, it will depart from you by Allah's permission. However, you must make up the prayers you missed due to waswasah, for they are a debt upon you.