ok, awesome. i'm glad you're trying to quit. don't ever quit trying to quit. seriously. do it. even if you can manage to smoke one less a day by chewing on something, putting something in your mouth (like gum or a pen cap, you pigs) or fidgeting with your fingers, it's a start. step down if you can't quit out-right.
i definitely know first hand drinking and smoking go together... i had to quit drinking, too, when my city banned smoking in public places (like the bars i fucking frequented!) before i could fully quit cigs. found a new vice... but i assume that vice is MUCH easier to have here in CA than LA. <.< ... >.>
as for your back, a couple things. lifting heavy from the ground and carrying heavy put different stresses on your back than being at the computer, slouching and having your arms out in front of you on a mouse/keyboard and/or carrying, leaning, walking around with and placing drinks. big boobs can be part of your problem (and part of the solution *wink wink*) but probably not the main stressor in this case. i say this because you've probably had your boobs for quite a while and the pain is a relatively new occurrence. (both my wife and daughter are well-endowed... i'm well-versed in both the pros and cons of plentiful pendulums, too

) oh and, in a prior life, i worked as a workers' compensation paralegal, so i'm very familiar with repetitive stress injuries and upper-back problems with folks who work/play at computers for hours at a time.
again, check your foot-wear... find something comfortable and made for all-day walking - there's a reason nurses don't wear high heels lol try to do some arm lift stretches before, during and after your shifts. rotate your arms at the shoulders, that kind of thing. try to keep your posture mostly correct when standing/sitting and keep your chin up, literally. looking down will also cause the weight of your head to pull on your already tightened upper-back muscles exascerbating your problem.
other than that, relax when you get home. take hot baths with bubbles, scents or soaps you like and just soak with your face toward the shower head or ceiling. you need to loosen your muscles if you can as much as you can.
oh and, did i mention stop smoking?
