Getting married - help

My fiancé is never in the mood for sex! He is too tired or makes excuses. We have sex once a week if I'm lucky. It is totally messing with my self esteem and we have one month until the wedding 😁 the closer it gets the more worried I am about getting into a sexless marriage. I've talked to him and he says I don't understand that he's tired. I am feeling desperate for advice as this isn't really something I can talk about with friends.