You seem to have back pain radiating to the leg. As you rightly surmised, this could most likely be due to a herniated disc or slipped disc. You need to consult an Orthopaedic Surgeon, who may prescibe Xrays or even an MRI. In the meanwhile, you should refrain from sitting on the floor or sitting crosslegged. Even in yoga, you should avoid floor exercises, and do only those exercises which you can do sitting on a chair,eg. breathing exercises.