Must I fast for two consecutive days after becoming pregnant, given that I made a vow for health, not for pregnancy, and I fear for my pregnancy? Is it permissible for me to delay fulfilling the vow until the pregnancy is stable, and must I offer expiation if I postpone it?

You must fulfill your vow by fasting two consecutive days whenever you are able, as long as your health is good after the examinations, because you made your vow conditional on that, and it has come to pass. Delaying the fast in order to take medication is permissible, and there is no blame upon you.