Canceling for the third time

So the guy I'm dating has being has seemed pretty off lately. He text me last night saying that he feels sick and he has to postpone out whale watch again for the third time. I am bothered that he keeps canceling. I'm at the point where I'm getting fed up. We don't see each other much. I want to answer to this text but I don't want to seem to aggressive or seem mad. How do I answer it