If you didn’t keep three fasts of Ramadan in the beginning i.e. you didn’t break them after starting, then only their qaza is wajib on you, not kaffarah (expiration). As kaffarah does not become wajib only due to leaving the fast of Ramadan rather it becomes wajib due to breaking it without a Shari’ah reason after observing. However, if, on the basis of your previous experience of increasing the illness, you did not keep the fast then you shall have to bear no sin, in-shaAllah. So it is mentioned in the books of Fiqh and Fatawa.
Allah knows Best!
Darul Uloom Deoband