You could have an allergy.
I used to get a lot of acne along the jawline and tried eveything too.
One day I was getting a facial and the lady said her friend had that and found out it wasn't really acne, but a dairy allergic reaction(not to be confused with lactose intolerance).
Needless to say, I stopped eating dairy that second, and the jaw acne went away.
On occasion I'll have a bowl of ice-cream, or something with dairy in it. About 24 hours later I'll have zits on my jaw again.
She also mentioned wheat allergies causing acne as well.