Did your doc check it out at your 6 week check-up?
I only ask because I had some pain after Liam and it turned out the stitches had caused tons of scar tissue which was actually affecting the vaginal canal. Thankfully, we did not try to have sex before the 6 week point with him, because I almost cried when they checked it at the docs office and found the problem. If you tore internally, even mildly, it can cause a build-up of tissue and that can cause pain. They fixed it, not prettily, but it still took time to heal after that. I don't have any pain any more, as the fix with kieran was simpler and did not have issues. I know Rachel had some of the skin buildup tissue problems I did/do, so I was wondering if perhaps you had some too and just didn't know it. I would expect that after 4 months it should be gone. I would get it checked out. Especially if you were still noticeably healing at your 6 week check. It could mean things did not heal up properly.
Either way, I hope it gets better for you. It is not fun to be in pain down there