Pregnancy symptoms 5 mo post partum

I’m 5 mo post partum with my second child. My husband and I had sex for the first time since baby was born about a month ago. Last night I woke with a terrible migraine and threw up. My lower back has been hurting as well. I do not want another child and I am planning on getting back in BC. I exclusively breastfeed and since I haven’t had a period I honestly thought I was in the clear. Has anyone gotten pregnant while breastfeeding? Please no negative comments. I know I need to take a pregnancy test but really what are the chances of this?