What Causes An Ingrown Lump Below The Collar Bone?

I have a black internal pimple in my upper chest right below my collar bone, its been there for about 2 years, i remember when it first appeared but i didn t mess with it because it was too hurtful to pop somehow it never really concerned me it doesn t hurt or anything i had forgot about it, but someone pointed it out earlier & i really don t know what it is, when i press it it doesn t hurt, i can feel the bump, its too internal i cant pop it out it looks blackish/greenish