What is happening to me?!... ghosts?

when i was younger my grandmother told me i used to talk to this little girl.. however only me my grandmother and uncle could see her cause he used to talk to her to.. now i am 17.. went to a "haunted" dam with my uncle amd his friends.. however something weird happened.. i seen a girl that wasn't there.. my uncle could see her to.. ever since then i have been having dreams of her.. then we walked into a local pizza shop. somewhere i haven't been in a year.. and there WAS a missing person picture up that has been missing for over a year. it is the same girl. one of my uncles friends have seen her once also at the dam. so when i showed him the picture it was the same girl also. he described a tattoo. mind you has never seen the picture before and wasn't on a missing person poster. we looked up missing people and the girl has the same tatto. however now he cant see her anymore only me. my uncle can on occasions why can only i see her and why is she pining me? what can i do for her