Making up for missed fasts
Q: I'm a convert to Islam, Alhamdulillah, a couple of years I did not fast in Ramadhan because I had really bad aneamia and I was underweight and whenever I tried to fast, I started getting sick. Weak/headaches/nausea. So I couldnt fast. Alhamdulillah my health is better now, and past Ramadhan I did fast. How should I make up for the years of missed fast?
And secondly, if someone is fasting and begins feeling sick and weak, is it allowed to break the fast without sin?