Something seriously wrong with my sweetheart. Everyone here please read this and help me! She's my everything.?

I'm 21 and my girlfriend is 19.We had been in this relationship for about 5 months and we even lost our virginity together,with each other about 75 days ago(i admit that we were a bit late though) until this happened 10 days ago: I was casually telling her that we should try other types of like as well and she didn't like the idea.She said "Ok.try it then,but i don't want to" and didn't smile after saying it.(WTF is she saying? try with whom? I just love her and don't want to even touch any other girl) A little while later,i took her out and we watched a movie together after which, we had a regular casual at my place and i was dropping her home on my bike.When i stopped at her home,we were playfully teasing each other like "you go first,no yo go,etc" Then,while she was going in,i grabbed her hand and kissed her fingers and she was like "enough for today baby,we'll play again tomorrow" and i was like "baby,can i tell you something" and gave her the most innocent look i could sport.She said "What's up with these formalities?" I answered,"Well,i'm not sure if you'll like it when you hear it" she squeezed my wrist perhaps unaware of the fact that she was holding it and looked at me a bit seriously and i could say by the look in her eyes that she was very uncomfortable. She said,"Spit it out!" and i was like "Baby,i want to be very open with you and hide nothing from you" she listened getting more closer to me and i continued "baby,i'm kinda obsessed with " and then,i paused for her to talk,but she didn't. She was kinda sad and i felt very bad about it and said "Ok,just kidding" She didn't look convinced at all. I then kissed her hand and she acted kinda strange by kissing me all over the face again and again and then ran in to her home and shut the door. I was puzzled and waited at the gate for 15 min and when i got no response,i headed back home,feeling confused and dejected. The next day at the college,she was late and i had to wait till the recess break to talk to her. I said "Hi sweet heart" and she just sported a fake smile in reply.I noticed that she was very upset about something and took her out to the park and we sat on a bench there. I cracked a few jokes to cheer her up,but in vein. I then thought of making it a bit hotter and kissed her hand and she was like numb.I then kissed her hair and was gently rubbing my face against her upper back. No reaction! I was getting a bit scared of something which i couldn't figure out. I put my head in her lap and stared at her for 5 min with total silence between us.She wasn't looking at me. I asked "What's wrong with you?" She just shook her head! I pretended it was cool and advanced to smooch her(she usually goes crazy with joy when i do it) and as i was getting closer she was still looking numb.I got very angry and left for the cl alone and after an hour as i was thinking what to do,i noticed that she was still sitting on the same spot where she had been when i left one hour ago. I stood hands crossed in front of her and asked her if i did anything wrong. She finally spoke "I want to go home alone today" I said with tears in my eyes,"What? Why?" and she said "Please go if you really love me" and i did as she asked. I'll tell you what happened next in another q or adding details as i can just type 4000 characters per post in my mobile. Meanwhile,please tell me Why she did what she did. Even today, I don't know why.