Stage 4 lung cancer

Hi just joined the group I was diagnosed with stage 4 lung cancer on the 29th April initially went to hospital with pain in shoulder blade which I thought I'd jarred at work that was at 9.30 in morning by 8 pm I was told the outcome I was totally shocked as were all my family initially started immunotherapy then went onto chemo found out on Mon at clinic cancer has shrunk so I'm going onto maintenance every 3wks the one thing I can't cope with is the weight I'm putting on it's really getting me down I know I should be grateful and believe me I am when I read some of the stories but can't get my head round it and it's really getting me down I've kept my weight the same for the last 8yrs as I follow slimming world so eat a sensible diet anyone got any advice TIA xx