One to one diet - cambridge weight plan

Hi, I was diagnosed in 2019, have had a combination of sulfasalazine, naproxen, hydrocloroquine, none of which really made a huge difference and have been started on cimzia since 2022 which has made a huge difference but I still feel like everything is such an effort if that makes sense, everything feels heavy, do very little exercise, only what is absolutely necessary.

Anyway to my point now I recently started on 121 Cambridge diet which is basically a calorie controlled diet using their products as put on a huge amount of weight since not being able to exercise and the difference I've felt is huge, I've only lost 8lbs so far but I'm not thinking is it the food I've been eating that has caused so much pain and heaviness all over my body. Anyone any experience of this? I'd be really interested in any info.

Thankyou