Snarg hit it on the head:
Quote:
When a girl is in a bad mood, oftentimes making jokes makes them feel like you are mocking them. Emotions such as anger or sadness are the body's way of naturally releasing this negative energy. By trying to make her laugh, it's causing an inconsistency in her mind that sparks confusion at an emotional level. This will have negative effects.
Women also typically do not want you to solve the problem or offer solutions. Instead, they want you to understand how they feel and comfort them with the sole fact that you are there for them. Pull her in, tell her you understand how she must feel etc, then kiss her on the forehead. When she gets over the severe negative emotions, that's when you can make a joke or take her somewhere fun to cheer her up.
Empathy is huge. Men understand the world logically (99% of the time) and women have the tendency to relate to things with more emotion. Emotion ≠ Logic... I promise it is not a linear logic, most of the time. Maybe try listening to what she's specifically upset about and relate to it as if you were in her shoes. Let her know you understand how she feels (if you understand) and say that you understand how shitty that can feel (if you get it)... if you don't, then really try focusing on what she's saying and at least be supportive to her (be very specific with what you're supporting).
I hope that helps (I've been in a relationship for over 20 months now and think I know a thing or two about what your going through)