It's perfectly normal for you NOT to be able to pull back your foreskin when erect - now. You should be able to when you get to be about 16 or so.
Yes, the head is very sensitive. The nerves have been protected your entire life. If you can, start letting your glans, the head, stick out a bit. Eventually you will get used to it.
Hope it helps.
You are normal for your age. Your foreskin is still developing. You should be able to pull your foreskin back when erect when you are older. You can start stretching exercises to speed things up.
Some guys have foreskins that have tips that are too narrow to pass back over the penis head. These foreskins may be gently stretched over a period of time to cause them to widen. When your penis is erect, gently pull your foreskin back against the head of the penis. As the head attempts to pass through the foreskin it will stretch the skin a little. Do this every day and in a few weeks or months your foreskin will widen and you will be able to retract your foreskin. Do NOT force retraction.
It works by tissue expansion. Stretching skin induces “mitosis” which is a word that means “division of cells”. New skin cells are formed and the skin expands. The increase in size is permanent. Be patient and let mitosis do its work.