B'Sha'ah tovah!
We hope that your nausea and hunger will have abated by Yom Kippur. In any case, unless your doctor feels that you are at high risk, it is imperative that you make every effort to fast.
It is also imperative that were you, G-d forbid, to take ill on Yom Kippur you would consult a rabbi promptly about whether to proceed with the fast. The rabbi you consult will direct you about drinking up to half of one mouthful at a time (measured before the fast by filling the mouth, emptying it into a measuring cup, and halving that) and eating up to 30cc at a time, both ideally at nine-minute intervals. If you do have to break your fast, have in mind while eating that you are fulfilling the mitzvah of "vechai bahem", living (and not risking life) for the sake of Torah.
Fasting on Yom Kippur is a Torah obligation and therefore takes precedence over praying in shul. (Your fast on Yom Kippur even takes halachic precedence over your husband's praying in shul.) If it will help you keep the fast, you could plan on spending the day in bed, resting and davening on your own.
As for Tzom Gedaliah, Asarah b'Tevet, Ta'anit Esther, and Shivah Asar b'Tammuz, there is a difference of opinion as to whether a pregnant woman who feels well should try to fast even though she is not required to. The Rema seems to indicate that the custom is to fast if it is not too difficult for her. However, the Mishnah Berurah states that a pregnant woman who feels any weakness should not fast.