Lost the flame

So my boyfriend and I have been going out for 4 years and I love him so much. When we were in university our sex life was AMAZING!! We'd have sex at least 5 times a week and every time it was mind blowing. Now it's hard to have sex even once a week. By time we get home from work and eat dinner were already so tired and he has to work to actually turn me on and vice versa. I was just wondering if there's a way that any of you guys know of that can ignite that flame again?