I would probably see a chiropractor or PT rather than a doctor at this point. They can help you on the road to recovery if there's nothing medically wrong with your back (slipped disc, fracture, etc.).
I bought my TENS on Amazon. They're really inexpensive. Your friend at work sound like he's become addicted to it!
Otherwise, ice/heat, anti-infamatories, good posture and mindful movements are all you can do. It just takes time--(and more time as we get older...).