Why her sudden crappy, more angry and not her attitude ?

So i've known this girl for around a month, we've been dating for half of that totaling about 4 dates, one initial meet up after i finished work one night (this is before the 4 dates) and once after she finished work.

She's arranged to meet me before her work tomorrow and she's on a night out on Saturday with friends and meant to be seeing me at my work and i will have to meet her friends, sounds good at first glance.

We got into the topic of 'what are we' in recent texts and she was joking about it, but i was more serious eventually i said i wanted to be exclusive, she asked if that means i'm her boyfriend now to which i said yes. But then she just said 'good stuff' and all today texting she has just been awkward and very out of character, changed totally from the texting whilst dating. Sounds like she's having ago and shitty small texts and just not being her. Surely if she wasn't happy or wanting a exclusive relationship she would have found a way out of that and wouldn't be discussing our next 'date' ? Its not like i've put it on facebook and gone over the top.

Maybe you gave in too easy. Or she just had bad mood and you had to deal with her as she is or cheer her up.