Hi have you actually had it confirmed its the MS HUG?
It could be Costochondritis(not sure i spelt that right). Costochondritis: Treatment, Symptoms, Causes, Recovery Times
Its very similar.
Never assume its your MS it can be something else. I would see your GP to just check especially as its affecting your walking and standing.
I have had the MS hug, it was like wearing a really really tight bra and for about an hour i could just about breath. I can imagine its like when you have broken a rib and they bind you up. then it just went. Hug doesnt normally last constantly.
like i said i would seek medical advice. x