All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
If you are temporarily unable to fast, then you have to wait until you become able to fast and then make up for the days of fasting that you missed. You do not have to fast the missed days consecutively; rather, you could fast them separately according to your ability. You could also delay fasting until the winter if this is more convenient for your health condition.
You do not have to pay an expiation in addition to the fasting of the days that you missed because you are excused of this due to your (previous) ignorance.
If your inability is a permanent condition that is not likely to end, then it is enough for you to feed a poor person a mudd of food per day of fasting that you missed. A mudd equals about 700 gm.
Concerning the feeding, it is not required to provide the food cooked at home. It is enough that you deliver a mudd of uncooked rice to a poor person's house.
The one who used to be ignorant about the valid way of performing the prayer is excused because of his (previous) ignorance and, consequently, the repetition of one's previous prayers is not required. This is the view adopted by Ibn Taymiyyah in his Fataawa; he discussed this issue and others, as he said:
"The sound view concerning all these issues is that no repetition is required because Allaah pardons errors made by mistake and out of forgetfulness. Allaah says (what means): “…And never would We punish until We sent a messenger.” [Quran 17: 15] If the teaching of the Prophet, sallallaahu ‘alayhi wa sallam, concerning a certain issue did not reach a person, then the obligation of acting upon such a teaching is not required from this person. ‘Umar and ‘Ammaar once experienced a state of janaabah (state of impurity due to having had sexual relations, a sexual discharge [due to whatever reason; a wet dream or other], or losing consciousness). ‘Umar did not pray while ‘Ammaar rolled himself in dust (performed dry ablution) and prayed. However, the Prophet, sallallaahu ‘alayhi wa sallam, did not command either of them to repeat the prayer. Abu Tharr used to have sexual impurity and stay for days without prayer. Moreover, the Prophet, sallallaahu ‘alayhi wa sallam, did not command Abu Tharr to make up for the prayer that he missed while he was in a state of janaabah. Additionally, the Prophet, sallallaahu ‘alayhi wa sallam, did not ask the companions to make up for the day of fasting in which they ate until the time upon which the white thread (of light) became distinguishable from the black thread (of darkness) (i.e. the start of actual dawn)."
Ibn Taymiyyah added:
"It is established by way of contiguous reports that there are men and women, in nomadic and urban places, who may come of age while not knowing that the prayer has become obligatory on them. A woman from among these may be told to pray; however, she may say that she will do so after she becomes old, thinking that it is only old people who are required to pray by the Sharee'ah. Also, there are many followers of Shaykhs (who belong to deviant sects) who do not know that the prayer is obligatory upon them. Such people are not required to make up for the prayers that they missed either, whether the reason is that they were disbelievers or that they are excused because of their ignorance."
With the aforementioned in mind, you are not required to make up for the prayers that you did not perform in the valid way. Yet, you must learn about the matters of religion that are obligatory to know. The more you learn, the better you will be in matters of your life and religion. The Prophet, sallallaahu ‘alayhi wa sallam, said: “If Allaah wills good to somebody, He grants him knowledge about the religion.” [Al-Bukhari and Muslim]
Allaah Knows best.