Why is my girlfriend so mad with me? birthday blues?

This year for my girlfriends birthday I made a particular effort not to ruin it for her as birthdays are special to her. I'm studying at the moment however, so I decided to go study for the morning and early afternoon so I could take the evening off with her.

She asked me at noon if I'd like to go shopping to which I responded that I would prefer to stay studying so that I wouldn't feel guilty about taking the evening off with her.

So anyway at 4 o clock or so, just as I had finished for the day, her manager called asking her if she'd work, which she did, despite knowing I was going to take her out.

She went to work and portrayed me to her manage as an asshole who treats her like sh*t (simply because I didn't open my schedule for the day for her) and they went on to bitch about me calling me names for the evening.

That evening when she finished work, I surprised her by collecting her and taking her to get a bit of fast food as it was midnight.

When I dropped her home she wouldn't even take any of the presents I had got her. I promised her to take her out for a proper dinner during the week.

The next evening, her and her manager discussed the presents resulting in her believing that "I don't know her" and me "not caring enough about her"

She got a lift home that night at 3 in the morning from her manager.

I think I treat my girlfriend exceptionally well. I do all I can for her and everything.

We haven't spoken since her birthday despite everything being great up until then. Its 5 days since this and I really feel like we're drifting apart and that our relationship (of 2 years) is coming to an end.

Any advice from anyone on what they think might be going on?

Why is my girlfriend so mad with me? birthday blues?
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