Welcome to HCM.
Acne( pimples) is a common problem in people who have oily skin and especially at your age. They often turn in to pustules due to secondary bacterial infection due to pricking or pressing. Benzoyl peroxide
is useful in treating acne. But if it does not give any response then preparations containing Retinoids
have to be taken. Using antibiotics like Doxycycline will help in treating infected acne. Do not squeeze the acne as it might leave a scar.
Based on the details provided you seem to be having Seborrhoeic dermatitis
. The reason for the pimples on the anterior chest wall ( cleavage) is dandruff
Anterior chestwall, nape of neck , interscapular area, forehead and the v area of chest ( cleavage) are the areas where the dandruff flakes tend to fall resulting in an inflammatory reaction there by leading to nodules or pustules and may end up leaving marks.
Treating the primary cause ( dandruff in your case) is essential. Using shampoos that contain Ketoconazole
( Nizoral shampoo manufactured by Johnson and Johnson) twice a week should help you. Apply the shampoo thoroughly to the scalp . This would definitely help you to get rid of this problem.
Even the marks would disappear slowly. In case if the marks are big and embarassing then using creams that contain allantoin
( hydroquinone cream should be taken only after consulting a doctor) should help you.
Hope you got the solution you were looking for.
Wish you a healthy life.