Hi Nordic and welcome to PC. I too experienced for many years similar issues in that I felt that being around people just drain me. Even now when I'm in a big crowd all I want to do is get out (unless I'm in India with my wife for some reason). The thing to try to remember and I know it's SO hard at times is that by and large, human beings ARE social animals. Our species survived and prospered because we HAD to rely on the group for survival. Nowadays it's not so important and people can live without other people being around but we still need people. We need the people who make computers and maintain the internet so we can login here. We need the farmers who grow the food and the stores we buy that food from. It's all people. We need the clothes people in the world make for us to wear.
It really sounds like your Dr. is asking this question to get you to ask it of yourself. Maybe not so much why you don't have someone but why you feel you don't want/need someone. As I said I felt like that many times until one day I met my [then] wife to be and it all changed. I need her now and since we had the baby, I really need him too. I'm guessing at some point in time someone outside yourself or family hurt you, maybe more than one and more than one person or said something hateful to you when you were small. In order to protect ourselves from that pain we build up these walls to keep others out but what we really do is cut ourselves off from the ebb and flow of all life which causes us to feel even worse at times.
Just search yourself and your spirit to find out why this question is bothering you so much and if need be ask you Dr. why he keeps asking.
I hope this has helped, if even a little.
Be well.
Chris