No energy

I'm soooo tired. I feel like I need a nap everyday. I'm sleeping 8-10 hours a night, my baby sleeps 12 hours at night. How can I kick this exhaustion without negatively effecting my milk?  
I also drink a cup of coffee a day, get plenty of water and food. Walk 30 minutes a day. Nothing has helped. My husband is getting really annoyed by it. I literally feel like my baby is sucking the life out of me.