Now that I added her what should I do next? (Ladies advice preferably)?

I was 18 and working at a grocery store, there's a girl I met that was 17 and started working there a short while after I started back in the Spring. We immediately clicked, we would get along so well and I also started developing a huge crush on her. So the second time I saw her, I asked her for her number. She giggled and smiled and gave it to me. We would text a few times a week throughout the Spring months. Then June rolled around and she graduated high school. (I'm only a year older than her, I went to a community college) and she was quiting her job cause she was going in vacation for the month of July and then going to school but only a little over an hour away. We went to hang out for the first time in June right after work, we went out for ice cream and sat outside on a bench together and just talked and had a great time. She called me a gentleman, and a copycat in a silly voice when I ordered but she had. Afterwards said she had so much and we had to do it again when she came back from vacation. We texted a lot while she was away, and then at the end of July I texted her and got no response, I tried a few weeks later and again no response, my phone has had issues cause I don't have much space on it (IPhone 5C) anyhow it's October and I found her on Instagram, I followed her and she followed me back. I want to inbox her, but I don't know what, I really need advice, I really still have feelings about her and I want to talk to her so bad, ladies what do you think?

I don't know what the ladies will advise, but I think she met some other guy while she was on vacation, and that is why you stopped hearing from her.