If you can’t retract the foreskin behind the head of the penis you may be describing phimosis, which basically is the inability to retract the distal foreskin over the glans penis (head of penis). Physiologic (or normal, naturally occurring) phimosis occurs naturally in newborn males. Pathologic phimosis defines an inability to retract the foreskin after it was previously retractible or after puberty, usually secondary to distal scarring of the foreskin.
Physiologic phimosis results from adhesions between the epithelial layers of the inner prepuce and glans (the skin of the shaft and head of the penis). These adhesions spontaneously dissolve with intermittent foreskin retraction and erections, so that as males grow, physiologic phimosis resolves with age.
Poor hygiene and recurrent episodes of balanitis or balanoposthitis lead to scarring of preputial orifices (the opening of the foreskin), leading to pathologic phimosis. Forceful retraction of the foreskin leads to microtears at the preputial orifice that also leads to scarring and phimosis. Elderly persons are at risk of phimosis secondary to loss of skin elasticity and infrequent erections.
Patients with phimosis, both physiologic and pathologic, are at risk for developing paraphimosis when the foreskin is forcibly retracted past the glans and/or the patient or caretaker forgets to replace the foreskin after retraction. Penile piercings increase the risk of developing paraphimosis if pain and swelling prevent reduction of a retracted foreskin.
With time, impairment of venous and lymphatic flow to the glans leads to venous engorgement and worsening swelling. As the swelling progresses, arterial supply is compromised, leading to penile infarction/necrosis, gangrene, and eventually, auto-amputation.
This may not be your case but I would suggest that if you can’t retract the foreskin easily or find it to be tight when the penis is erect you go get checked out.
Hope this helps.