Brief Answer:
Its basic anatomy
Detailed Answer:
Hi
Thanks for using healthcare magic. I, Dr Abhishek Kapoor, would try to help you in this query.
I think, first i would like to give you some basic knowledge about anatomy of penis.
Inside penis, there are muscle which are covered by foreskin. The enlarged and bulbous-shaped end of the penis is called the
glans penis, which supports the foreskin, or prepuce, a loose fold of skin that in adults can retract to expose the glans. The area on the underside of the penis, where the foreskin is attached, is called the frenum, or
frenulum.
During non-arousal state, muscle remain flaccid and it is easy to retract skin from glans penis. But at time of erection, if skin is attached with glans penis due to frenulum, it would not retract after certain level. May be in your case, frenulum is still intact.
Don't worry with regular sexual activity, it would tear down own its own, but that time it could cause pain and bleeding.
I think, there is nothing serious in your case. It just misconception or lack of knowledge about basic anatomy. In case you need further help, you can connect me.
Regards
Dr. Abhishek Kapoor
Psychiatrist