I'm 6 weeks postpartum as of 7/14, and had sex unprotected 7/15 but got period back 7/18, is pregnancy possible?

Possible butunlikely: Your vaginal bleeding on 7-18 at 6 weeks after a pregnancy may resemble a "period " but be due to various causes. If you had unprotected sexual-vaginal intercourse with a fertile man, "pregnancy is possible". A blood betaHCG pregnancy test will answer your question. If it is negative, consult a caring and knowledgeable gyn about an IUD or a subdermal implant ASAP . Protect yourself,use condoms too