My Boyfriend Sleeps all the Time. What do I do?

So, my boyfriend sleeps a lot.

About 85% of the time that I spend any amount of time with him, he either is asleep when I get there or he falls asleep at some point. This is majorly cutting into my time with him, and he is always irritable when he wakes up. This is the biggest strain on my relationship with him (not necessarily his relationship with me) currently. Today, for example, he called me at 9am seemingly excited to do some errands, and hang out with me today. When I got to his house at 10:30am, he was asleep. I finally decided to wake him up at 11am, and he wouldn't get up. Now that he's finally gotten up he has an attitude with me.

I KNOW that he gets enough sleep at night. We spend the night together at least 3-4 times a week, so I know for a fact that he is sleeping a normal amount at night (anywhere from 7-9 hrs). The other nights I'm not sure that he's getting enough, but I highly doubt that he is going to bed super late those nights.

I've told him once that this is becoming a problem (about two weeks ago). He told me he would work on it, but nothing has changed. I don't really know what to do.

Any advice or suggestions welcome!