Numbness occurs due to nerve compression either at Lower back level of spine. Different reasons can be there. Also nerves can get entrapped under tight soft tissue structures below the level of spine. The exact cause can be known by an Orthopedecian and/ a Physiotherapist after a proper assessment.
Next Steps
Avoid the positions and/movements which cause numbness and visit an Orthopedecian and a Physiotherapist if the need be!
Health Tips
If you need to life some weight, keep it close to body. Sit and stand (while lifting weight) with back straight.