absolutely need help!!!

So on may 12th my daughter will be 5 months old. I exclusively breastfed up until a month ago when my milk stopped and later found out that I wasn't producing hind milk.... long story. However after lochia bleeding and six week check up I started my period while still breastfeeding. However alarming it was to me I brushed it off and my dr told me that it can happen. Well my husband and I decided that we would like to try again because we want our children pretty close in age. I'm asking how long is the extra fertility window after pregnancy and is it possible that I could be pregnant if my period starts in two days? I'm sorry for my ignorance but I've never felt a need to track me cycle until this past year. Any help would be awesome! Thank you!