welcome to health care magic
I will try to answer your queries
1) Shyness could be a part of your personality or social phobia
2) Yes there are many effective treatment strategies for depression
like antidepressants, psychotherapy
3) Psychotherapy - CBT (Cognitive Behaviour Therapy
)... Consult a psychiatrist/psychologist
4) Loss of appetite could be a part of your primary illness
5) Maturity comes with experience. Don't repeat mistakes in life. In that way you can attain it.
However, these all problems are linked to one primary diagnosis for which psychiatric consultation is required.