I’m sorry to hear you’re going through all this. I was 39 at my de novo diagnosis with children of 2 and 6. That was 2020 though. I haven’t had growth yet and don’t do any of the diet stuff you mention so please don’t think for a second that it relates to anything you do. The cancer is just a sneaky wossit.
I would get a second opinion. I would have thought your oncologist should be testing you for mutations, like PIK 3 A, as that might be why the cancer has grown and it opens up more treatment lines. Not sure if you’ve seen this before, but some are here: Treatment Lines - METUPUK
I do find exercise helps my fatigue. I hope you enjoy the yoga. I find that and reflexology help my aches and to relax me and I think the latter is important as the mental side is tough and we do need to try and minimise stress.
Anyway good luck for your appointment and please let us know how you get on.x