I'm going to confront my girlfriend
What is the confrontation about?
I'm going to address her lack of interest in sex.
It is fine that you are upset with your partner, however be sure to discuss the issue in a civil way. Relationships are all about talking and about growth, so if there is anything that is bothering you it is great to get into the habit of talking about it anyway.
I know I should but I just get frustrated when we have sex and she doesn't show any interest.
It can be frustrating in the moment but that is why you should have the conversation at another time. You should calmly discuss this when you are not upset and it will help the conversation not get out of control.