Hi,
I suggest making an appointment with a gynecologist, for a pelvic exam. You may be having difficulty with penetration and pain due to either a thick hymen, an extremely small vagina, or vaginismus ( involuntary vaginal muscle contractions that can make penetration almost impossible & painful). A doctor would have to examine you to determine what is causing the issues. While you're with doctor, be sure to explain the problems you are having. Sex and penetration shouldn't be painful, and it should definitely be pleasurable for both of you. I hope you're able to find an answer soon.
Take Care