My daughter was in Intensive Care for 3 months and lost 4 stones. Before admission she enjoyed healthy meals, was a healthy weight and slim so you can imagine how frail and weak she looked with loss of both muscle and fat.
A dietician saw her and advised me to give my daughter a minimum of 6 small, high Calorie meals a day served on a tea plate so as not to overwhelm her. Long time ago but I remember protein drinks, crisps, cheese, hard-boiled eggs, Jaffa cakes and nut butters were recommended.
My daughter had daily physiotherapy for a few weeks after which she continued at the local gym and I got hold of an exercise bike which she rode daily too.
She had little appetite and needed lots of encouragement but progressed well gaining 2 lbs every week.
Nowadays she is well and loves exercise, particularly cycling and recently did a 160km bike ride for charity.
Good luck and I hope your strength returns soon.