fire burning out

so my husband and I have been married for three years, I for one have always been a very sexual person and he was too at first but lately he just comes home from work and is too tired to do anything if we do have sex it has to be me on top because he's literally too lazy. i understand he's tired but he hasn't gone down on me in 6 months I don't know what to do, I feel like the fire in our relationship is burning out. I'll take any advice I can get.