Why is my girl being this way?

Ok, so I've been dating Sammy for a year now. I've just got into boxing and everything and started doing some rounds with some partners. At first she used to make fun of me, saying things like "Oh, you're so hot without your shirt" or "You're dancing around like a girl!" She used to be okay with it. I was a lot skinnier when we first started dating but I've filled out greatly since workouts. But recently, she looks upset whenever she's at the gym with me. I keep asking what's wrong but she says nothing. I know its not that I don't spend enough time with her, and I remember our anniversary, her birthday, and always take her out. I talked to her friends Brittany and Jackie and they said it's something about my boxing matches. What's wrong with her?