Thanks for the query.
There is possibility of some abrasions and post-coital tears inside the vagina.
These may not be visible outside.
As you are having pain, once consult gynecologist and get examined to rule out above factors.
And also check for any possible pelvic infection
Using lubricant analgesic
jelly like xylocaine
jelly or KY jelly etc. during intercourse, which will help in lubrication and in decreasing pain.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429