ITs unfortunate but a lack of self confidence is quite noticable especially if you are keeping your head down and not making eye contact.
The problem with having hang ups is that the majority of the problem is in the sufferers head, Im not making light of your problem!!, but when someone meets a total stranger most of the time they barely notice the thing that you feel so conscious of.
Or at least they actually dont treat it with the huge amount of importance that you do, In fact the problem with having hang ups about specific things is that the more you try to hide it the more of a big deal you are making it, so in effect your making the problem bigger by being so affected by it.
You probably have a soft spot for the doctor partly because of his complimetary comment but also because he has seen past the acne scars.
Eye contact is something that if you stop doing it can become a habit to not do it at all, making eye contact again will do your self esteem some good and stop you looking so down at heel.
my brother is autistic and hates making eye contact, he gets by this by just looking at one eye or the bridge of the nose and making brief eye contact at the end of every couple of words.