You may have to have this corrected surgically. My friends teenage son had to have surgery to correct his because his was too tight too. Ask your doctor. I wish you the best.
First step would be to try prescription topical steroid creme treatments with foreskin stretching. There are certain techniques to do this and in lots of cases surgery can be avoided. It is a procedure that takes about 6 weeks twice daily for yourself to apply. I know we can not advertise here but we found help through norm-uk and in general, do some research by googling Phimosis. Many times it is acquired phimosis that either happened because of infections or inflammations or because the foreskin had been retracted forcefully too many times as parents used to be instructed to do which can result in scar tissue which in turn can lead to phimosis. Whatever the cause, it sounds like you would have good chances with the steroid creme. But you will have to see a doctor for the presciption at least and it would be good to be under a urologist`s supervision who can track the success, however it can be a catch 22 as many of them are only to eager to perform surgery, circumcision that is. Get lots of information!