Wedding crisis!!!

Please help! My fiancé want to plan our wedding and I'm extreamly scared. As soon as we get married he wants us to start our own family. But I'm extreamly unhealthy. I'm obese but my man doesn't care how I look. But I care about the big day and I also care about my health and my future babies health. I need help. I'm about 75lbs overweight for my hight. Im ready stressed and I want to be a healthy weight by the time we get married so when I try having kids my weight isn't a health problem I have to worry about. Any advise? Please anything.