Hi Joyce,
Yonkyo is supposed to hurt.
That's what causes the attacker to submit. At what level of pain the attacker will give up varies somewhat so it's important to be aware of when to stop. No need to piss off your partner.
On the other hand, as attacker, it is also important not to "fall" before the pain comes, otherwise it never becomes a learning experience.
In this particular instance, "No pain, no gain" seems appropriate.
Try not to shy away from the pain because yonkyo hurts. Instead, look forward to the day people collapse at your all powerful Vulcan-like touch!
Good training,
Eddie