Fasting during the month of Ramadan is one of the five pillars of Islam that are of paramount significance. The Prophet (peace and blessings be upon him) said, “Islam is built upon five pillars: testifying that there is no god except Allah and that Muhammad is the Messenger of Allah, performing Prayer, paying the zakah, making the pilgrimage to the Sacred House (Hajj), and fasting the month of Ramadan” (Al-Bukhari and Muslim).
A person who is chronically ill is exempted from fasting, but he or she must offer fidyah (compensation) for that. Compensation for skipping a fast is feeding one poor person. Allah says: [For those who can do it (with extreme hardship), is a ransom, the feeding of one that is indigent] (Al-Baqarah 2:184).
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: If your physician is a trustworthy person and he or she has advised you not to fast because of your peculiar medical condition, then you should act on the doctor’s advice, for Islam does not allow us to torture ourselves. Allah has revealed laws that are primarily intended to help us remain healthy and sound in mind and body. Allah says while prescribing fasting on the believers, [But he who is ill or on a journey shall fast (a same) number of days later on) (Al-Baqarah 2:185). If, however, there is no hope for the sick to recover, then they should offer fidyah (compensation), which involves feeding a poor person for each of the days of Ramadan fast one has missed.
So if you have a reasonable hope that you will recover from this condition, then you ought to make up the fasts you have missed later on. If, however, yours is a permanent condition, then you need only to offer fidayh as stated above.