What Causes Sudden Severe Pain In Back Radiating Towards Groin Area?

Had severe sudden pain in my back radiating down to my groin 2 weeks ago and went to doctor. She checked me and thought it was muscular. Gave me injection to relieve pain which worked ok that night. Following week took it easy but on and off pain again. Now I have a tender spot on my back but numb type sensation in my groin which is constant. Is this likely to be still muscular?