Is it permissible to postpone making up for missed Ramadan fasts from previous years until next year due to suffering from obsessive-compulsive disorder (OCD) related to creedal matters and the desire to seek treatment first?

You must fight off whisperings (waswas) and ignore them. Scholars differed regarding making up missed Ramadan (definition) fasts (qada'). The majority of scholars are of the view that it is obligatory to make them up before the next Ramadan. However, Abu Hanifa held that it is on time-at-large (al-tarākhi) and there is no sin in delaying it. This view is suitable for someone afflicted with waswas. It is advised to fight off waswas, hasten to make up the fasts, and not pay attention to whisperings about the invalidity of the fast.