Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
The sickness that permits the person to break the fast is the one that makes the person undergo much hardship because of fasting, or the one that is feared to worsen because of fasting, or the one whose cure may be delayed because of fasting.
So, if the sickness you are suffering fits into any of the above categories, then you are permitted to break the fast. But you should make up the same number of days you did not fast as soon as Allah cures you. That should be done – if possible – before the coming Ramadan. Now, if you delay making up such days with no excuse, then you should make up the days and feed a needy person for each day you did not fast.
But if the disease is chronic and there is no hope of its cure according to trustworthy doctors, you are not asked to make up for the days you did not fast but you should pay a Fidya which is feeding a number of needy people equal to the days you did not fast. The Fidya is estimated at 750 grams of the food that is mostly consumed in a given area.
Allah knows best.