The reddening of of the index finger of left hand with burning sensation indicate the inflammation of dermal vessels.. called vasculitis
It may be without cause ..idiopathic or may be due to some cause..like trauma, infection or some internal disease.
In your case,you are having other symptoms also ..headache, vomitting, diarrhoea
. May viral or bacterial. This may be the cause of vasculitis.
You consult dermatologist
and physician for perfect diagnosis and treatment.
I hope you got my answer.
Dr. Ilyas Patel MD