Look, its really hard. And I myself am certainly not one that is good at being told what to do hahaha! The time will probably come when you will have to say something subtle like, I really appreciate your concern, but I really do need to move around a bit/clean this desk/do this filing, (or whatever the case is for your job) because not moving for too long makes me feel uncomfortable and I need to get the blood flowing, but would you mind moving these boxes/files/carrying this for me, or something along those lines. I am not sure what you do for work, I am a legal secretary so we are in the middle of an office reshuffle in our group and 3 of my lawyers are moving offices, no way in hell I will be packing boxes and crates let me tell you lol. And I haven't told them I am pregnant yet, other than the woman I job share with, and she tells me what i can and can't do from a distance. leave that for me, I will do it next week, don't you worry about that, i will sort it out next week. Don't you dare do any archiving, I will get to it when I can. She is lovely!
You don't want to offend anyone because you have to work with them, so its hard to find that middle ground where you can tell them to buzz off, but get them to do it carrying stuff for you at the same time lol