I have been exclusively breastfeeding for 4 months, when can i expect to have my first period after delivery? will my period effect my milk supply?

It varies: It may take some time although as the child starts eating solids and you are offering less breastfeeding then it is more likely your periods will resume. It is not your period that will effect your milk supply. It is actually that as your milk supply dwindles you will then start having your periods

Varies: Great job on the great feeding! Keep it up! Your period may not start until you stop breast feeding. However, it could start earlier to. It varies from woman to woman. If your period comes, your milk supply should not be significantly affected if you are consistently breast feeding. Keep up the great work!