Is there some type of supernatural presence in my house

To start off, I am deathly afraid of supernatural stuff like this. So, my parents had this big new house built on my grandparents property a few years ago. All was cool in the beginning, of course I was kind of nervous in my new room, being as I was only like 12. I'm almost 16 now, btw. Anyways, so as soon as I got comfortable in my room, stuff started happening, of course. One night I was trying to go to bed and I heard the door open; I thought that it was just me dog at first, as he likes to come upstairs and sleep. But when nothing happened, I got up and shut the door entirely. As I was walking back to my bed, there was a loud bang on the door, which almost scared me to death. Hesitantly, I approached the door and opened it, since I thought it was one of my brothers. Well, one was snoring loudly on the couch (he wasn't faking, either) and the other was way away in his room with the door locked. Suffice to say, I slept with the light on. So life kind of continued on like normal; I would have terrifying dreams and have to leave my room, my dog would go upstairs and bark at nothing, my mom heard my door slam when she was the only one home. Stuff like that, enough to totally terrify me. So recently, my mom told me that she would be lying in her bed and something would lie on the bed next to her, against her back. At first she thought that it was just my step-dad but when she turned over, no one was there. This has happened a couple of times. And, I just found out, lucky me, that one night when I wasn't home, my step-dad slept in my bed (my mom snores really bad) and was sound asleep when he heard the door open. At first he thought someone was going to play a prank on him, but there was no sound. Then he said that it felt like someone had sat on the edge of the bed; he laid really still and then turned real fast to see who it was. No one was there and the door was closed. Wonderful. So I have been researching stuff like poltergeists and found that quite often strange stuff happens to teen girls around puberty (me apparently); I thought that this was right at first until I realized that that wouldn't work because if that was happening, it would just happen to me. Not to the others in my house. So, sorry that it was really long, and there is probably some things that I forgot, but if anyone can please help tell me what's going on, I would be very grateful. I don't think that it's a ghost too because some grandparents have lived on this property forever and no one has died on it, except for maybe some dogs. They aren't dead either; my parents built like a second house for them that is connected by a room to ours.