Could he have been too tired, like he said?

I am a bigger girl, 5'5 and 220 pounds. I am seeing a pretty skinny guy, and we've been having sex regularly. I feel as though he may be getting bored. We tried to do it doggy style to switch it up, but he couldn't comfortably get it in. He says that he's never done doggy on a bed, usually elevated areas. So we went back to missionary, but he couldn't orgasm. I've never had issues satisfying my partners before, some have been smaller than him. He is very into satisfying me, which isn't an issue, he gives me multiple orgasms regularly, but it's hard to be satisfied knowing your partner wasn't. Could he have been too tired, like he said? How can I spice up our sex life to keep him satisfied? What kind of positions and tips could I use to keep him and I happy?