Sometimes when I first sit down I have this horrible throbbing (heart-beat) back pain that lasts for several seconds.

History: I am 4 1/2 years clean and sober. Back when I was drinking etc. I had this a lot and thought it was probably my kidneys. But it went away after I got clean and sober. I am very active now and work at a hospital where I do a lot of walking etc.

I am now being treated for a severe bacterial infection, bed rest, antibiotics etc. but this has returned. The pain is sometimes almost unbearable.

Any suggestions on what might be causing this again?