I hope I can help guide you here, understand though that online its impossible to state with certainty what ANYTHING is, especially with skin issues. All I can do is give my best educated guess based on what you've written.
Urgent matters first. I am really concerned with the fact that you cant retract your foreskin; total inability to retract it is rather dangerous because it is possible that the tightness of it can restrict blood flow to the penis, potentially killing tissues and damaging its function. You do not want that; the medical term for this condition is called phimosis (total inability) and paraphimosis when retracting it is possible, but very difficult. Here is more information on this: http://emedicine.medscape.com/article/442617-overview and a non medicalese reference: http://www.intelihealth.com/IH/ihtPrint/WSIHW000/24479/10520.html?hide=t&k=basePrint
Its possible you could have a fungal or bacterial rash. Rashes on the head of the penis are called Balantitis. And they can as I stated be either bacterial or fungally caused. Balantitis, IF fungal, can be treated by over the counter anti fungal creams. HOWEVER, I do not know 100% that it IS a fungal infection (or even that it is Balantitis). Fungal infections tend to more red, and more spread out.
Balantitis can also be caused by bacteria; if this is the case it would need antibiotic ointments or oral medications (depending on severity).
MILD cases of balanitis, IF fungal, can be cured by over the counter anti fungal cream. However, given that you can not retract or move your foreskin, this seems to be rather more than a mild case, and I think you should be seen at your doctors as soon as possible for appropriate diagnosis and treatment; this could be bacterial which requires oral prescription antibiotics. IF your foreskin can not be retracted, that is a good reason to GO TO THE EMERGENCY ROOM.
Here is a helpful website regarding balantitis: http://www.nlm.nih.gov/medlineplus/ency/article/000862.htm
Images of BACTERIAL caused Balantitis: http://www.dermnet.com/Balanitis-Bacterial/ You will see it refers mainly to uncircumcised men.
I hope that was helpful,