So tired after orgasms...why?

It is easy for me to orgasm, intercourse and masturbation. But the thing is, I get very tired the day after. I'm only 27 and it has been like this the past year or two. Before that, I could have several orgasms and wasn't tired at all. Now I feel I have to sleep 1-2 hours in the middle of the day, because I'm exhausted. Why am I getting so tired now? Is there someone who can relate to this?