Is low self-esteem, a brain chemical imbalance problem, rather than a personality defect, and can't be fixed by any amount of counselling/self-help? I am asking this question because I recently observed something within myself:-

I think I used to be a Borderliner plus Bipolar. I was very sensitive, and slightest of events will either induce mania in me or will just thrash me into severe depression and low self-esteem.

But since I am taking a certain medication, I have observed that I am now not experiencing above mentioned behavior within me. I am much more resilient to criticism.
Low self-esteem can be the result of severeal things, implying depression and other mental disorders, past experiences (harassement for example). We can "fix" low self-esteem through non-drug therapy, but sometimes we can't. There is no fixed answer, it varies from person to person.



My personnal experience : 
I am a schizoaffective and asperger person, for me, self-esteem is something really instable because of depressive/hypomaniac phases and schizophrenic symptoms. It is not something that I can control, except with high medication.

Sources and readings : 


Low self-esteem and psychiatric patients: Part I – The relationship between low self-esteem and psychiatric diagnosis
Low Self-Esteem Is Related to Aggression, Antisocial Behavior, and Delinquency
Self-Esteem and Adolescent Problems: Modeling Reciprocal Effects