Don't bother with a paranormal investigator. The 'professional' ones will tell you whatever you want to hear as long as you pay them, and the real ones (unpaid, actual researchers) won't even come out based on the stuff you mentioned. There's nothing even unusual going on, let alone ghostly or paranormal. Let's look at your specific occurrences...
Things fall off of dressers and walls all the time, due to a well known phenomenon known as gravity. We don't think of gravity very much, but it's always there and never takes a break. Gravity will pull and pull on something, light or heavy, until it wins. In the history of everything else vs. gravity, gravity has never once lost. It's hard to claim that a ghost did something fall when gravity is around.
That feeling you get, that creepy feeling that something is watching you and about to attack, is actually a good thing. Or at least it was, way back in history. Big predators did and still do exist in the world, and we were on their menu. Take a look at our natural defenses some time, and you'll note that we don't have any. We don't have sharp teeth or claws, we're not fast or very strong, we can't climb very well, our night vision just plain sucks, and we don't even have thick hides or armour. Big predators, on the other hand, have it all: They're fast, strong, have sharp teeth and incredible night vision, and they know when to attack. They attack when their prey is alone, they move in from behind, and they'll wait for that perfect moment (always watching from the shadows) as long as they have to.
Since we have no physical defenses, our massive brains learned that avoidance and evasion were the best way to survive. We can't out-power our natural enemies, but we can out-think them. We know to avoid being alone, especially in the dark or in places with a lot of blind spots, because that's where the things that eat us like to attack. Of course you and I know there are no tigers or packs of wolves inside your house, but your DNA doesn't care. That being-watched feeling is what kept our species alive for thousands of years, so your body isn't going to get rid of it just because we've learned to build houses to protect us.
And let's look at this girl you saw/felt next to your bed. You said you never looked, so actually you never saw her. You did, however, get that creepy feeling (you know I'm right) while in bed and glimpsed something out of the corner of your eye, and it looked like it was a girl, but then you were afraid to look. It's OK if that's what happened, because that happens to everyone. I'm a guy who will stand up to two tough dudes in a bar without showing fear, but I've had that thing-beside-the-bed experience too and I was afraid to look. We all get that feeling.
Even though you saw shadows moving, that doesn't do you any good (or bad) unless you saw what caused them. Shadows are perfectly natural things, caused by anything between where you are and the source of light.
You see where I'm going with this? You're taking a bunch of stuff that happens naturally, all the time, and building a theory around it. Your dad doesn't believe you, but only because the stuff you're describing is totally normal.