It is haram for a traveller to break his fast when: 1- he is travelling but the distance does not reach the distance at which it becomes permissible to shorten the prayers, 2- his journey is not permissible, 3- he is travelling in order to break the fast, and 4- he is travelling and wants to break the fast before leaving the houses of his village or city.

A pregnant Muslim woman is obliged to fast unless she fears for herself or for her baby, in which case it is permissible for her not to fast. For more, please see the detailed answer.

If your sickness is one from which there is the hope of recovery, then after you recover you have to make up the fasts that you missed. But if your sickness is permanent and there is no hope of recovery, then you have to feed one poor person for each day that you did not fast.