Why girls think a lot when they are in a new relationship?

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I am in a new relationship recently,but once he doesn't give me a call or send me a message ,I will think a lot.I'll guess whether he doesn't like me.or maybe he is busy now.I just can't stop thinking of it. I even can't sleep!Perhaps I'm sensitive.But why girls always think too much,how about boys? Will they do the same things as us?