What Causes Difficulty In Retraction Of Foreskin?

i am an 18 yr old guy with 3.5" penis when soft and 5" when erect with no sexual experience. I cannot retract the foreskin of my penis fully only halfway when erect but i can, with lukewarm water when it is soft(not erect). In normal condition its just covering the whole glans .Every part of my glans hurts when i just touch it and it appears pinkish white in colour. A reddish ring of swollen mass is formed when i retract the skin fully which is situated just above the retracted skin . I can't get my penis erect for a long time let alone ejaculate after this. Am i hurting my penis even using warm water ? my penis just feels lifeless. it loses erection if i try to retract the skin while erect . what can i do to cure it. i have also seen sphegma under my skin. Is the swollen ring due to infection? when will i regain my full erection. what problems will i face if i am going to have sex and what are the cures. How much skin retraction is normal and how much should i try it and for how long and when should i try it without hurting my penis?