Breastfeeding and conceiving

I am currently 4 months postpartum (counting down to the 18 month mark when we can start trying for our final child) and lately I have been having constant weird vivid dreams that I am pregnant. I am exclusively breastfeeding and we are careful but I am not on birth control due to complications it causes with my body neurologically. So with that being said, I suppose my question is, with a 4 month old exclusively breastfeeding 10-12 times a day how easy is it to become pregnant? I've taken a test recently so I know I am not currently. If it does happen we will do our best to cross that bridge then and ensure the safety of both baby and myself, but having just had a c section, I'm concerned about what it may do to me.