How to turn him down when he asks for a second round

I usually have around 10 papas (male supporters). I don’t dislike sex, and I’m very attentive, so I used to agree when they asked for a second round, but lately it’s become physically too much and I’ve started experiencing health problems. My papas tell me, “You’re different from other girls—you don’t seem like you’re having sex reluctantly, which is nice,” but for the sake of my health, I’d like to start turning down second rounds from now on if possible. How can I turn down a second round without making things awkward? Actually, I think I’m pretty skilled when it comes to taking the lead, too. But I’m worried that if I seem experienced rather than passive, my papas might not like me as much...