hi..thanks for your query
From the above description , I feel that you have might developed a ringworm infection on the neck area.also known as , Tinea corporis
, it is a superficial fungal infection characterized by either inflammatory or noninflammatory lesions on the skin.Topical antifungals are available OTC in most countries and you can do a 2 weeks therapy of the same.
however if you feel that it is increasing rapidly, or not responding to only the topicals applied ,you may need an oral anti fungal therapy for the same.Please visit a dermatologist
for this, as the actual nature of the lesion can only be understood on observation .
hope this helps..take care!