What could the spot on my neck be?

(Firstly sorry if this is a weird question but it is worrying me.)

I have a weird spot on my neck about the size of a fingernail (and a similar spot on my arm which no longer stings) which appeared within a day. It doesn’t hurt as per say but it stings if you press it. The strange thing is it is a bump in the skin which is not red or anything, it is just the same colour as the skin around it. Also if I press it it feels as it there is a ball under the skin…

Any ideas as to what this could be?