Ask her, if you dare – “What do I say or do that displeases you?”
If she gives you a blank look or a half-heartened answer, prime the pump a bit. The list could include phrases you use, nicknames, what you wear, shows you watch, and on and on.
Now that you have the list, what on that list are you willing to stop doing – completely stop doing – to make her happier? Yes, I’m talking about sacrifice here, and yes, some women would take advantage of this. However, imagine how she will feel if she gives you half a dozen things that displease or bother her, and eliminate even a couple of them? Moreover, if you stopped doing all of her list – how would she react to that?