What Causes Sharp Stabbing Pain Above Ribs After Doing Lifting Job?

hi , for the last 4-5 years i have been in ajob where i am lifting up to 27 kg all day and i have had, and now they are getting worse up to 3 0r 4 times a day, up from 3-4 times a week, sharp stabbing pains just at the top of my ribs mainly on the left hand side, they are now moving around to my side also. two doctors have said it's muscle /chest muscle but it wont go away, i had x rays on wkend they were normal, apparently, i would like to see maybe a specialist i am getetting concerned now ?..