What Does Blister Or Cyst Like Bump Behind Ear Imply?

I have a blister or syst like bump behind my ear, it is sore and feels pressured like it is filled with fluid it is in the crease on the back of my ear where it joins my scalp
I have foolishly thought it was a pimple and poked and squeezed it, some puss came out.There has been a bump there for a few months but it has recently gotten larger and very sore