if you really don't have a boyfriend, say it with sincerity. people might take your words as a joke. maybe you should first wait for someone to ask you whether you have a boyfriend or not. you might not want to push to someone that you don't have a boyfriend, don't you? :)

does it matter?it is your personal problem,i think it has nothing to do with others or others' opinions

Yeh it is credible .Why wouldn't one believe you ? I think it is a rhetorical question. Maybe some of your friends or colleagues show you signs of surprise that you don't have one ? Well it is alright if you don't have one at the moment. You might have your reasons and as Sophie says your friends should appreciate you for who you are ,if they don't then you have to doubt their friendship in the first place . So just don't feel forced into getting a boyfriend or you would hook up with the wrong guy. There might be sort of a peer pressure when you see most of female friends having their boyfriends. I think you have to know what you want . If you don't feel at the moment like having one or because you didn't really meet the suitable one so don't rush in ;)

It is more important to be happy with yourself first and not to rely on somebody else to bring you happiness. Your friends appreciate you for who you are and not the fact that you are plus/minus boyfriend. Enjoy life. :)

Don't care if people don't believe you and why are they must interfere other people love life? Never hurry and rush for love. You are young and carefree person. Think something you can do. Mix around with people and make some friends .