First of all, thank you for your question. Although we cannot give you medical advice on this matter, here some information that might help you.
If you do not have problem while masturbating, there is no reason why you should be worried about it when having sex with someone. However, if you feel that the foreskin of your penis is too tight, we might consider being circumcised. For this, you should talk to your doctor.
Whatever it is, the pain is abnormal. Make sure that you wash your skin located under your foreskin regularly. If you are unable to bring it down because of the pain, it might be because there is smegma that accumulated, and it can get infected. Talking to a doctor will reassure you on this matter.