You may eat or drink as necessary on the fasts of the Tenth of Tevet, 17^th of Tamuz, and Tzom Gedalia if you are sick, faint, or dehydrated, but only enough to resolve your health difficulty.  Consult a rabbi.

All fasts start 72 minutes (normal time) before sunrise except for the Ninth of Av and Yom Kippur.  These include:

• 17th of Tamuz
• 10th of Tevet
• Tzom Gedalia
• Fast of Esther
• Fast by a groom and bride on their wedding day
• Fast for first-born males on the day before Passover. This includes first-born cohanim and Levites (levi'im).

You may brush your teeth on Yom Kippur and all other fast days without water and without toothpaste.  (You may not use water to brush your teeth even on Tenth of Tevet and 17^th of Tamuz.)

Here are the times when men and women are forbidden to get haircuts and men are forbidden to shave, including their necks (from most severe restrictions to least):
Most Severe Restrictions

• Mourner for parents (no shaving for the first 30 days and no haircut until three months after his or her previous haircut).
  Note If mourning for other relatives, you may get a haircut after 30 days.
• From Saturday night before Tish'a B'Av until the evening after Tish'a B'Av.
• Chol ha'moed.

Next Most-Severe Restrictions
Shiv'asar B'Tamuz (17^th of Tamuz) until the evening after the Shabbat preceding Tish'a B'Av.

Least-Severe Restrictions
During 33 of the 49 days of counting the omer (sefirat ha'omer); that is, either from the second day of Passover until Lag Ba'Omer (33rd day of the omer) OR from Rosh Chodesh Iyar until the day before Shavuot, according to your custom.