Thank you for your query.
As your son is on hormonal
replacement therapy the testosterone
being given is having its effect on the testicles which can explain the symptoms. However severe pain
in the testicles can occur because of other reasons too and it is advisable to show him to a doctor to exclude any other reason like torsion of the testicle which may require surgical intervention.
I hope I have answered your query to your satisfaction.
Wishing your son an early recovery.