How can I stop myself from constantly crying over not having/never having a boyfriend at age 21?

I have never had a bf and I am 21. No guys ask for my phone number and a guy has never asked me out. Sometimes, I do feel lonely and I will find myself crying over never having a bf and especially when I see other people so happy in relationships. When will it finally be my turn to find love? Yes, I am a shy girl and I do try to go out a lot and people say I am a nice girl. But I just want to share my life with someone special.