Mihlar,

If you feel that you need your medication or by fasting your body/health is at risk, you dont have to fast. BUT you will have to feed a poor person for each day of fasting month. The same ruling for pregnant or breastfeeding women.

As for travelers and women experiencing MP, they have to make-up for those days missed once ramadhan is over.

Those not required to fast are 1. A mentally ill person 2. Old person 3. Children under the age of 15.