During , experiencing pain?

I have been in a long term relationship for many years now. In the beginning i never experienced pain during but for the last 2 years i have! It happens most of the time, i feel a sharp pain of some sort when he enters & even during sometimes i feel a very light burning sensation. I am well lubricated down there so i don't know what the problem could be? Some times the pain lasts throughout the whole time and sometimes only the first 5 or so minutes. Can anyone tell my why this is?