No , it is because there is no chemistry in you. The problems lies with you. You are not talking and interacting with people (of both gender) enough. Most guys nowaday are not boyfriend material , it is really hard. Ya true. Make more friends.
I'm gonna go with the latter of the two, lol. You just haven't found the right guy yet. I know you've probably already heard this but just be patient. The right guy will come along sooner or later. Good luck (and I hope its sooner) :)
Well your question very general, so I am not sure what you are looking for. Without knowing a lot about what is going on with your situation, I may not be able to give the greatest advice. But in general, don't worry about trying to attract a boyfriend or change your ways of acting to get a boyfriend.
When it is time for you to have a boyfriend, you will find one. He will come to you and it will just click. You are only 19. You have your whole life to have a boyfriend or husband. Why worry about that now?
Be young and have fun. Date around and see what is out there. Find out what you like and that way when you do find it, it will be that much better. Love takes time, so don't rush a relationship. You just haven't found the right guy yet. Hope that was helpful to you.