Its most probably due to nerve compression in the lower back area because of disc bulge leading to the pain in the leg specially at the back side of leg(called as sciatica).
Next Steps
go for physitherapy..ultrasonic therapy for healing,tens for muscle relaxation and heat therapy for reducing inflammation may required . take rest. then the exercises are to be done and very much important.
Health Tips
For back-at home.bed rest for seven days+hot water fomentation+application of pain killer gel..avoid forward bending, weight lifting, cold exposure , stair climbing.long travelling or driving, no prolonged standing/walking/sitting.