Why is this happening between her and I?

Im at a loss here. This one girl and I used to talk so much. I liked her and when I found out she liked me too I asked her out. Though ever since asking her out I feel we have become more and more distant. She never texts me first and even just flat out ignores them when I do text her. She also doesnt even make the effort to do anything with me. I have tried taking the initiative but when I do she never seems to have time. I just find this weird because I am her boyfriend and I feel a bit offended that she cant even make the time to talk to me let alone do something with me. Does anyone have any idea what is going on? I know she likes(ed) me because her bestfriend told me how much she wanted to start a relationship with me.