I had coccyx pain well before I started letrozole and it happens now after I have extended days sitting...like flying then a conference etc. Exercise is the best for it and stretches. Laying on your back knees up but feet on floor. Bring one leg up and rest ankke on thigh and press your knee outwards. It stretches the hip flexes. ..which if tight limit the coccyx. Repeat on other side. I have arthritis all through my spine which gives me no pain unless I sit around too much.
I took fish oil for around 8 months. Panadol osteo for around 4. I think the taxol contributed to my pain to be honest. I rarely need it now.