Can I complain too much because I am a little frustrated?
That depends. What's frustrating you?
Well it is clear that my girlfriend doesn't like me that much and I would like her to say exactly what the problem with me is instead of denying everything.
Couples are expected to have an open line of communication. If you suspect that she no longer cares for you, then you should come out and ask her why. Because if you keep this held in, your relationship will suffer and possibly end.
I know I should ask her but remember what happened last time we had a fight.
But if you hold it in you will just grow more and more resentful. You should just tell her what you are feeling and resolve it instead of letting it fester.