Can you get pregnant from precum if you are breast feeding?

Yes: Any time that you have vaginal intercourse, there is a chance of pregnancy! be sure to use protection- condoms and another birth control method every time if you do not wish to get pregnant.

Potentially yes: Most studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile (however, don't know how promptly samples were examined). One small study published in 2011 showed that there are some individuals with a high motile sperm count in pre-ejaculate. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564677/