How many days must be made up from last Ramadan's fasting, given the doubt about the number due to illness and taking medications?

One who is able must make up for missed days of Ramadan, based on the Almighty's saying: "But whoever among you is ill or on a journey [during them] then [he must fast] an equal number of other days." If the exact number is not known, one should fast until certainty of fulfilling the obligation is achieved. It is not permissible to delay making up the fasts without a valid excuse until the next Ramadan begins; otherwise, an expiation of a mudd of food for each day becomes obligatory. However, if the delay was due to an excuse, then only making up the fasts is required after the excuse is no longer present, with no expiation.