Why does she want to call my attention after ignoring me for so long?

So I met this girl some time ago in a class we had, when we talked I reaally thought that she liked me, I mean she was giggling, laughing at what I said, being really friendly and helpful etc. Any how next day, she was acting very different, she was ignoring me and it seemed she didn't want to talk to me at all. I kept trying but it was useless, I think I was pissing her off at one point. So I just stopped talking to her.

However just recently she has trying to get my attention as I have seen her looking at me and she has also trying to get close to me, she doesn't say anything but I know she wants me to talk to her.

Do you guys have any idea what is going on?
Why does she want to call my attention after ignoring me for so long?
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