Priscilla,
There is no simple answer regarding medications and breastfeeding -- it all depends on the medication. At the bottom of my article
Nursing While Sick I include links to two books regarding medications and nursing. The Hale book is thought of as the "bible" in this respect.
Be sure to let your doctor know you are nursing and you may be able to find a solution that works. La Leche League often has access to doctors who can also help if yours in not knowledgeable on drugs and lactation. See my article
Finding Help - La Leche League.
You may also want to consider seeing some alternative practitioners -- a nutritionist, herbalist (lactation knowledgeable), homeopath, naturopath or acupuncturist and see if you can deal with the symptoms you are experiencing with dietary changes or other remedies that do not affect lactation.
Good luck! Thanks for stopping in...
Nicki :-)