Hi,
Welcome to ehealthforum.
Causes for painful intercourse include vaginal infections, dryness or lack of lubrication, PID, vaginismus etc. Treatment of infection, use of proper lubrication, couple therapy/sex therapy can solve the problem.
I would recommend you to get yourself examined by a gynecologist to assess the vaginal tone and tightness (and also rule out above mentioned causes). If it cannot be loosened with exercises/manual stretching, you will need to discuss about options of vaginaoplasty to help you with it.
Take care.