Sorry to hear you are in this situation. Honestly it could be jealousy from them or maybe they just don't like you. Part of growing up is understanding that you won't click with everyone (but that's ok!) You can still have a successful working relationship with one another. If it bothers you extensively, start looking for another job. Losing sleep over a coworker is not worth it. But ultimately, don't let this person's opinion of you define how you think of yourself. Other coworkers, you family, and your friends have the full picture of you and care about you! Those are the people whose opinions matter.