Boyfriend is tired

So my boyfriend works a lot and when I go stay with him we don't have sex a lot. I stayed the entire week and we only did it twice. Sometimes when I try he rejects me and says "I'm tired" which I understand because he works 12 hour shifts 6 days a week. Should I be worried though? I like to have sex a lot and I understand everyday is unrealistic but every other day would be nice.