Suggest Remedy For Back Pain

I have a history of lower back pain, to include throwing my back out about once a year for the last 3 years. Recently its gotten much worse and I have thrown my back out 4 times in 6 months. 2x not very severe, mostly a minor strain but the other 2x i couldnt walk for at least 3 days and was out of work for for a week each time. The last time my back went out severely was about a week and a half ago and i can walk and move around now but I still feel a lot of stiffness and discomfort in my lower left side of my back and and after sitting for more then 15 min, when I get up my back is very stiff and my left leg, behind the knee, has a lot of pain. I can barely stand after sitting because of this. Ive seen my Doctor twice and both times I was prescribed meds and rest. Ive also seen a chiropractor/physical therapist in this time. Neither have helped much except the meds for the immediate pain. Ive had an x-ray which came back negative and have been back at work but am worried pain will not get better and ill have another back issue. I work in Law enforcement and cant afford to always be worried that my back might go out again at any minute. Any advice as to what this could be and what future steps I should take. My Doctor keeps telling me it should go away but here I am still in pain. Thanks.