Hi dear, good you are in final stage to get doctorate. I can understand you are feeling of low confidence, thats ok, have you any time tried introspecting yourself for low confidence and the reason that you are not able to answer the question? do you have any high expectation or you are not able to accept the situation. normally low confidence is that: people are scared to do any work, feeling they might do wrong or thinking that opposite person might feel that they lack in knowledge or anything. connecting to this may be you are not able to communicate freely with others in which it is resulting in social anxiety. yes you can visit psychologist or psychiatrist they will evaluate and help you in different issues you are facing. take care. stay positive. best wishes.