My girlfriend can't orgasm/squirt......?

We're both 18 and both each other's first, but she doesn't like being eaten out or fingered. Just rubbed occasionally and if I'm lucky, we'll have sex. We usually do once or twice a week and we started doing it about 3 months ago. The only problem is that I think I'm getting her to semi-climax because after she "has an orgasm" she is all tired and tells me to stop, but honestly I don't think she is. Any suggestions?