Should I be frustrated at my significant other for not having sex with me?
Have you let her know you want to have sex with her?
I've demanded that we have sex but she refuses.
You can't demand sex from a person, it's their choice whether they want to or not. You'll just have to be patient and wait for your girlfriend to be ready for intercourse.
I can't wait. I want to fuck now.
If she's not interested in sex right now, then you need to be patient with her. If you love her and she loves you, then she will be ready again before you know it and demanding does nothing but make her wait longer.