Were you able to pull it back to the extent to fully expose the glans of penis before?
if you were not able to pull it fully back from before it could be phimosis. you need to consult a general surgeon regarding this issue as this will require circumcision. circumcision is a very small procedure which takes not more than 10 mins to perform.
if you were able to pull it back before and are not able to pull it back now, it will need to be examined to comment as to what is wrong.
so, you will have to consult a general surgeon itself.