Hi there ~
I understand your concerns. I believe that the while mass under the penis skin or the foreskin like you mention it is probably an infection like molluscum contagiosum
or commonly called as genital wart
. It seems like you are having this issue for a long time and it can be cured with topical medication
. Please consult a dermatologist
so as to get the lesion examined and have it treated. I hope this helps.
Take care and have a lovely day!