I don’t usually respond to posts often but I felt that maybe it can be helpful.
First of all I don’t intend to be hurtful in anyway and if anything I say may hurt you then please forgive me.
One needs to look into themselves and write down the reasons that one thinks he/she is a nerd and try to see if it is a valid reason or just some perceived notion based on x amount of times that people have told him/her or made him/her feel like he/she is a nerd etc…. (Also alot of this might have to do with ones upbringing schooling etc…. so it can really take time to figure these things out.)
Once one has the reasons that he/she thinks that he/she is a nerd, he should go through them and see if there are things that he/she can change. For example if one tends to be forgetful and puts his glasses on top of their head and forgets that he/she put them there and then looks for them for an hour and finally finds them, one can think to themselves” Boy am I slow…. I am such a scatter brain… etc…. etc….all these are negative feelings which lead a person to have negative thoughts and low self esteem which eventually leads to being anti social and then leads to depression G-d forbid. but if one learns to do things to help oneself not get into this situation it will help him/her reverse this effect and to build a better self image etc…
One has to believe in themselves in order to succeed so after he/she devises some sort of plan to change what can be changed and to accept that which is hard to change I believe that he/she will be more ready to believe in themselves.
I am sure that I barely covered this in depth as there is a lot more out there and there are a lot more possibilities of what the problem might be related to. Usually these issues are related to low self esteem and reading books on how to develop better self esteem will be helpful.
Last but not least one needs to ask Hashem to help him/her see the truth, to be happy with who they are and to be able to change the things that can be changed and to accept the things that cant be changed.