Issues in my married life ( wife not interested in sex,........)

Hello, My name is Hosahalli Ananth, i am from Bangalore, Karnataka. I have few queries regarding issues in my married life, request you to advice me how to proceed further. 1> My wife is not interested in sex with me : My wife is not interested in sex with me, its not for few days, its been for months. If it was because of some issue like period time or her getting tired in office, i could understand. But recently during a fight, she told me that she is not interested in having sex with me. We have been married for 4 years now, the married life has been a troubled one right from the beginning and so was the sexual life with her. Finally to get a child, we had sex. I am not sure if has any feelings and just did sex with me for the sake of getting pregnant. Now we have a boy of 1.6 years. Every time i go to her for sex, she says some reason like i am tired or i have some infection and i did understand her problems and was fine with that. But here comes the main point, she is putting this blame on me that i have some weakness and i do not have any feelings for sex. Now my question is, if she is not interested in having sex with me, its fine. I am ready to continue this life with her because of the baby as i am attached to him a lot. I want her to legally declare or some legal documentation to be done which states that she is not interested in continuing sexual life with me, so that its very clear that its her who does not want to have sexual life with me and i do not have any sex related weaknesses or problems which is trying to make out. 2> The second and also a main important thing, she does not want my child to take my surname and she fights for that. Is it any special thing that i am expecting. Any child would have fathers surname as his surname. Please suggest me on how to go ahead, going for divorce is not feasible for me as i do not want to loose my son as in most cases custody goes to the mother.