I had a spinal block for csection on may 4th and have recently started having serious back pain, especially where the spinal was inserted. why?

Unlikely related : If it has been more than six weeks after your surgery, I would not expect for the spinal block to have suddenly caused a problem. More likely after your delivery you've become more active after a period of immobility and with more movement are now experiencing back pain that may just be muscular. Try stretching, heat and ibuprofen.