Why does she do this?

So my girlfriend and me have been dating a little more than three months. She'll usually text me most if the time first. She'll text me a few days acting all flirty and keeping the conversation going or whatever. Then she'll stop texting me, which is fine because we both decided we don't have to text everyday. So we usually don't talk for a few days. When I text her first most of the time she never replies or she'll reply hours later and send short replies that makes it hard to reply to. And sometimes she'll text me first, but just never reply back the whole day, which makes me think why even text me, you know? Now I never do that to her, I always reply as quick as possible. I understand she could be busy or whatever, but it's literally almost every time I text first. I only send her the first text too. Another thing is that I've asked her to hangout a few times and she says she can't each time, but whenever she asks me I do. We hardly hangout too. Sorry it's long, thanks!