Thanks for writing to us.
Firstly an inflammation of scalp can lead to swelling of neck lymph nodes. Hence you are having a bump on neck. It will resolve spontaneously once the scalp gets back to normal.
Itchy scalp with rash and similar involvement of forearm could be due to seborrheic dermatitis
. Use of antifungal shampoo like ketoconazole
every alternate day with application of steroid
lotion should help you out. Use an oral antihistamine like cetirizine
to control itch.
Hope that helped.