Loti, Star is dead right.
You need to find ways of saying to everyone, including the girls, 'No, that's enough - I'm busy doing a) x (for me)b) nothing' and variations on it. I say this lots. I play lots too, and do stuff for dh and work, but they all know that they can ask so much of me and then no more: 'Thus far and no further' as Parnell didn't quite say. And if they don't listen, I just talk louder and roar if necessary.
Hard as it's going to be you need to stop giving people permission to disregard what you want, need and feel. That sounds awful, but your health really is at stake here and we so want you to feel better in every way. There are so many issues at stake here: Star is spot on - with your apologising your actually asking us to disregard the distress you're in. That kind of habit, from what you've said before, goes back a long way from you and it'll take work to break it.
Please, please understand we're right behind you. If you want to chat on t'phone at some point, just say. But we're just so worried that you'll grind yourself into the ground and or keep allowing other people to do that for you. 