sounds to me like your troubles are exactly the same as mine
mine is caused by the broken vertebrae that were fused back together again (i think i've got an xray somewehre) and limit the movement

i think you've probably over done it with the caber carrying lark and now the muscles that are in agony are being helped by the other muscles in the area, but because they are getting used far beyond their normal capacities, they are also struggling which is causing you more pain

a few tests that iwas told to do when this sort of pian accoured was to stand up straight, feet together and then bend forwards as if trying to touchmy toes, but not actually making the effort, just letting the body hang there and natuarlly stretch out
you "should" feel the stretch in the back of your neck and in your hamstrigns, anywhere else in your back means it's something in there so at least you can localise the area of pain

obviously if your rib is the limiting factor in this then don't do it, but you'll need rest for a few days at least

for some home cure attempts, stand in the shower for a while with the jet on hot on the painful area, and also adjust the way you sleep, if you have, i've found that putting a doubled up duvet on the mattress and laying on that tends to reduce the pain as it lets your body relax a bit more than it would on a normal mattress that's a lot firmer

if the pains not abated much by tomorrow then i'd be making my way to the docrots to get myself looked at properly, the pain killers you are taking just mask the pain, if you've torn a muscle it may take a long time to heal properly