Unsure How to Eat to Achieve What I Want

Previously weightlifting and healthy eating have worked pretty well for me. Having now had my second baby and breastfeeding this time around I have really lost myself through it all and gained 7kg since birth 6 months ago . Obviously, I’m not a genius but I know exercising with weights will go a long way I just don’t know how to eat because of the baby’s nutritional demand. Above everything the health implications of being overweight bother me and I’m not sure how to regain and maintain a healthy weight without giving my child formula which I don’t wan’t to do. Any advise is really really welcome, thanks.