Feeling lost!

I need help! My fiancé and I want to have a baby but because of A school and what not I don’t really get to see him. I know it takes time but I kinda feel like it’s my fault we can’t get pregnant. I’m over weight and no matter what I do I can’t seem to lose the weight. People keep telling me it’s a big thing. What should I do? Any tips? Maybe sex positions will help? People help.