Is it stinging? You might be having little microtears. Just take it very very slowly, lots of kisses before to make sure you are ready.
It could be a touch of vaginismus which can become a bit of a problem as it sort of becomes and catch 22. I have this and vulvodynia for years. Have a Google of it and see if it fits. It's an easy fix if you think it is that, happy to discuss on pm if you want to
Have you consulted a pelvic floor therapist?