Certainly after four months a diagnosis needs to be made. It could be muscular is not good enough in my book.
Do two little tests for me. First, lying on your back, pull your knee to your chest, and then the opposite shoulder, and then make a circle with the knee. Same both sides? No pain? Just to rule out a hip condition.
Secondly, lying on your back again, open your legs and ask your husband, using a generous amount of cream to run his thumb up the inner thigh to the inferior pubic ramus, and then through the groin towards the hip, being careful of the femoral artery. Compare sides. Is the left much more tender? Where? Bone? Muscle? In groin?
I would presume this is in some related to the chronic coccyx pain you have. Probably an old fall on some part of the pelvis, now forgotten.
The femoral nerve also supplies this area, but you make no mention of back pain, and I have a feeling that's not the case. But it could be a radiating pain from your back. A femoral nerve stretch test needs to be done.
Then, it could be something gynaecological. The deep pelvic muscles attach to the pubic rami and can certainly be a source of pain down yonder.
So the question. Is this a chiropractic problem? To do with the sacroiliac joint or coccyx perhaps. Or is it a medical problem, perhaps the bone itself, or for a gynae? Perhaps to do with your ovaries, bladder or uterus.
What's needed now is a careful thorough examination by several doctors from different fields. An X-ray of the pelvis would be a good place to start.
You are right to be concerned. Don't continue to be fobbed off by your doctor. Take hubby with you next time, and demand answers.
Let me have answers to above tests.
I hope this contributes.