What specifically is the danger or risk of lifting more than 5-10 lbs after breast reduction surgery?

I had Breast Reduction surgery on Aug 19. I was instructed not to lift more than 5 lbs. for 5 weeks after that. While sitting in my office chair, I've been pulling (& pushing) an ~35+lb box back-&-forth out from under my desk, sliding it along the floor, pulling it towards me. Does pulling (or pushing) a heavy box along the floor like that while seated in a chair count as lifting more than 5 lbs??? If so, what are the potential problems of doing that???