Happens Possibly due to a nerve compression at the lumbar level of spine. PLease do add more information if last week you had a fall or any kind of incident that affected your back area and also what profession are you in also does matter . The Occupation of yours has a greater impact on your back.
I will advise you to consult an Occupational Therapist and if possible provide some more information,
unless and until the nature of incident is known , I shall certainly avoid prescribing you any exercise regime, else there are pretty good chances of worsening the condition.
You might have to get an CT /Xray done / visit neurologist . that all can be told once history is known regarding the problem.
Next Steps
Get Consulted by Occupational therapist or may provide details at Practo.
Health Tips
DO NOT UNDERESTIMATE / NEGLECT PAIN AND WEAKNESS. STAYHEALTHY