You need to eat properly and rest. Your body is only just coping with the recovery from illness and you are stopping that happening by stressing it with dieting and exercising so it can’t repair itself.
When I diet I always feel cold, don’t know why but it’s common for dieters.
Eat a bit more, better balanced diet, few more carbs too. Knock the cycling back a fair bit.
If you want to be riding for decades to come to you need to stop for a bit now. Not stopping could ensure you may increase the risk of not being able to cycle ever again if your body doesn’t recover.
On a lighter note Ton, you rode past me near halfords this week as I was walking back to my car from work. Your Surly looks amazing in the colour!