Rest frequently during the day and continue breastfeeding as usual.

At “Afur” when you break your fast, eat fresh fruits and drink a glass of juice or milk shake. Limit “Sambosa” (deep fried pastry) or “Mandazi” (deep fried sweet bread) to not more than a serving.

Let your dinner be like your “suhoor”. Be sure to include milk and vegetables.

Avoid fried foods at “Suhoor” and “Afur” as they increase thirst, reduce your milk supply and make your fast uncomfortable.

Limit caffeinated tea or coffee to 2 cups a day. Drinking too much tea or coffee makes you lose body water and increase thirst.

Fruits and vegetables help prevent thirst, and maintain breast milk supply."

and

http://www.missionislam.com/ramadan/prepare.htm

"Pregnant and breastfeeding women have special permission not to fast during Ramadan if they feel that they or their babies will be harmed by it, but they are not prohibited from fasting if they feel they can handle it. This is something best discussed with a doctor and depends on each woman's unique circumstances. However, it is very important that pregnant and breastfeeding women take care to eat properly during non-fasting hours if they choose to fast. It is also important that women do not feel any shame or guilt in breaking the fast if they feel they must; no one has the right to put pressure on the pregnant or breastfeeding woman to exceed her body's limits. In fact this allowance not to fast should be considered a mercy from Allah and not a punishment.
Likewise, women should not fast just because they do not want to have to make their fasts up later: health should be the prime consideration in deciding whether or not to fast. Take the fast one day at a time: it is not a competition with others but an act of worship for the sake of Allah Most High.

Of course women who are ill or must take medications during the day need to consult their doctors in order to see if it will be possible for them to fast and to change the schedule of their medications. Discuss the issue with a sheikh if you are not sure about your situation.

Whether a woman misses days of fasting due to menstruation, childbirth, pregnancy, breastfeeding or illness, these missed days should be made up before the next Ramadan comes. Insha'Allah. Depending on her circumstances and on different schools of thought, making up the fast may be as simple as fasting one day for each day missed during Ramadan, or it may require that she feeds one poor person each day either in addition to, or in place of, fasting herself. Women should consult reliable books or scholars to understand their obligations in this regard. Fiqh us-Sunnah by As-Sayyid Sabiq is an excellent source of reliable information on how to make up missed days of fasting.

Understanding and respecting your body's physical needs and limits during Ramadan will help you to have more energy for taking care of your home, family and other responsibilities."