Breastfeeding does increase your energy and fluid needs somewhat, but it does not require a restrictive or special diet. A varied, balanced diet supports both you and your milk. Drink enough to satisfy thirst rather than forcing large amounts, and keep water handy during feeds.
A vitamin D supplement is often recommended for breastfeeding parents, and some continue a prenatal-style multivitamin. There are usually no foods you must avoid, though limiting caffeine and being mindful of alcohol is sensible, as both pass into milk in small amounts.
If your baby reacts to something you eat, discuss it with a healthcare professional before cutting out major food groups, since unnecessary restriction can affect your own nutrition. If you follow a vegan or restricted diet, ask about vitamin B12 and other nutrients to make sure both you and your baby are covered.