I know how you feel.. I just had three weeks of insaneness and I went off my plan bad and did not exercise... I felt down..
but much like mandalinn said what CAN YOU do????!!!
I know with a sore back that makes thing more difficult.. but even focusing on something like building or toning your arms muscles or your shoulders.. or your legs will get you at least moving those parts of your body but giving your midsection like back and abs a break so your back can heal. doing something simple as doing a few reps of arm curls with a water bottle or holding a can of soup if you don't have weights will help you build your strength!
Also make sure your getting plenty of sleep and try not to stress too much because those things can hinder your weight loss.. also try and drink the recommended amount of water daily!
Oh and GREAT job on cutting back on the smokes! before you know it you'll be off them completely!
good luck things will get better!
Love,
Maria