Hi.
Read and understood you query. Thanks for an elucidate history too.
You are right , this obviously looks to be a pimple, sebaceous
cyst in medical language. Once this gets infected it shows all the changes which you have correctly noted, namely
redness, tenderness, fixation to the surroundings.
I would advise you the following::
Consult a General surgeon.
He would confirm the diagnosis by clinical examination.
Prescribe you antibiotics and anti-inflammatory medicines.
Surgery for removing the mass and the pus in such a way that recurrence is avoided. Simply giving an incision can cause this to reappear at a later date if the inner lining is not removed.,
Take care, go for the right Surgeon and the most proper treatment . ...