Pregnant and nursing women do not have to fast on the 17th of Tammuz (or on the other minor fast days – the 10th of Tevet, Tzom Gedalyah, and Ta'anit Esther). There is some disagreement as to whether they may fast if they feel up to it. They should conduct themselves appropriately for the mood of the day by eating primarily in order to avoid hunger rather than for pleasure.
On the Tisha B'Av and Yom Kippur, normal, healthy pregnant and nursing women fast just like anyone else. The difference between the two days is that the fast of Yom Kippur is d'oraita (Torah mandated) and that of Tisha B'Av is d'rabbanan (rabbinically mandated). Thus, a woman who is sick or very weak may eat on Tisha B'Av, but she may not eat on Yom Kippur unless it is dangerous for her to fast. Each individual situation should be discussed with a rabbi.
For either Yom Kippur or Tisha B'Av, if your physician feels that you should not fast for health reasons, you should consult with a rabbi prior to the fast. If you feel more ill than anticipated during the fast, you should ask the question again. A woman who has recently given birth should certainly ask a question in advance. Depending on the circumstances, it may be either prohibited, permitted, or required for her to fast. On Yom Kippur, she may be instructed to eat normally, to eat "b'shiurim" (small, measured quantities), or to fast.
The prohibition on marital relations applies to Tisha B'Av and Yom Kippur. On Yom Kippur separate beds are required. On Tisha B'Av they are recommended. On both days, hugging and kissing are prohibited because they may lead to intimacy. However, touching, passing, and other activities restricted during niddah are generally permitted during the daytime.