My life is falling apart...I don't have a girlfriend and my grades are failling.. Advice?

I am 19 years old, and I am a student going to a community college. I work in retail part-time also. I am really bad at making friends, and now it's really bothering me. I am trying to make guy friends, but I really want a girlfriend. I never had a girlfriend before, and it is really bothering me. I hate being single. My father's family is always bad-mouthing me for not having a girlfriend. At the last get-together, they bad-mouthed me, until I started crying. My 2nd cousin is my age, and he has a girlfriend. My brother is older then me and he also has a girlfriend. So at get-togethers it's always me without a girlfriend. I'm always the one without a girlfriend. It is so painfull not having a girlfriend, and I can't stop getting upset about it. I really want a girlfriend, and I am failling 1 of my cles and i already had to withdrawl from another cl. My grades would be better if I had a girl. I don't really know any girls right now good enought to ask them out.