Thanks for choosing XXXXXXX for your health related query.
I think you are having inability to retract your foreskin back over the glans
.This is called Phimosis if the inability is total , and Paraphimosis
in case of partial difficulty. For normal sex, the skin has to be pulled back fully for penetration. Phimosis results in painful penetration and infection of glans beneath the skin, due to lack of hygiene. Your infection will be transmitted to your wife, causing discomfort, as reported by her. but if you wear a condom, the penis is able to penetrate .
You need to consult a urologist
. he will correct it by a minor surgical procedure, called Circumcision
. It is a day procedure, done under local anaesthesia and need no hospitalization.
Probable it is not due to tight underwears.
Hope this helps.
DR SAATIISH JHUNTRRAA