Recently I noticed sores on my dogs head, his head was quite lumpy with them and his hair seem to be coming out with the scabs. Yesterday after wondering why our small dog kept going and what seem to be nit picking I looked for myself and could see what seemed to be a large open sore. My father said it looked like a cyst, but its quite big , there is now no hair round the area.  I have sprayed something on it to try and keep the other dog from going near it.
Any ideas what this could be??

See the vet.