Thanks for writing to H.C.M. for your query.
I have gone through your query regarding itchy throat and nose with a big red spot on left arm, this spot is hurt on touch but not itching at all.
Considering your complaints it appears as you are having allergic rhinopharyngitis,and yur big red spot on left arm may be of allergic origin, or it may bedue to someinsect bite or may be traumatic.
You are adviceto take-
as an analgesic
(c) Warm saline gargling.
I hope this will help you. otherwise consultation with your doctor will be necessary.