Friends trying to get me to date

I am a 19 year old guy, in my second year at college and studying physics. I have never had or been interested in having a girlfriend. I have felt awkward for a while when ALL of my friends started dating people, and I was the only person left single. I considered dating to fit in, but I really didn't like anyone at all. People seemed to accept that I wasn't dating anyone and didn't bother me about it before, but now that has changed. It started with one of my friends, who kept telling me to date people, jokingly at first.
Now most of my friends are telling me that I should get a girlfriend. I can't figure out why they are suddenly starting to do this, as they weren't bothered by me not having one for the last six months. I keep telling them that I am not interested, but that doesn't stop them. Is there anything I can do or say to get them to stop, because saying that I am not interested doesn't seem to work?

It's not working when you tell them because they are not taking you serious and in a way, they don't respect your opinion. My friends stop bugging me about it long time ago, they know me well enough that that's my prefer lifestyle and they even ask me for relationship advice ironically. It's because they respect me. If you want that respect, you have to stand your ground with them when they step out of line. You can't let them push you to do what they want. Respect is earned, remember that. So next time your friends are being disrespectful to you by pushing you to get a girlfriend, remind them. And with any other interaction you have with them, never let them push you around. Over time, they will value your integrity and stance and will accept you for who you are. And with friends who does nothing but gives me problems, I cut them out. I don't carry around unreasonable friends. Life is too short to let it rule by others.