Thanks for the query,
You are probably suffering from pustular acne
It is a moderate variety of acne and often involves the back and neck.
The other possibility is recurrent folliculitis
You may require treatment with oral antibiotics
as pus means infection.
Please meet a dermatologist
for exact treatment.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.