Under Attack?

I have lived in this apartment house for five years. It is a very old place, built in the late 1800's and has served as an army barracks. Later in the early 1900's it served as a hotel.
Now this big house is divided into four rather large apartments. I live in the top right apartment, and a few good friends live right across the hall. Each of our apartments seem to have extra inhabitants.

It all started with knocking on the front door every night at 2:13am. When I installed the doorbell, the doorbell would ring about that time. It actually scared the crap out of me when I saw someone standing there in the flesh one time! But it was my friend across the hall asking me if I had just knocked on her door. But it wasn't me, and the doors at the bottom of the stairs were still locked from the inside.

I have seen shadows here from time to time that have no explanation, but nothing compared to what I saw three weeks ago.

I was laying on the couch watching TV when my cat and kitten came running in and both jumped on my lap. I laughed and said, "What are you doing you silly kitties?" At the same exact moment they both looked into the hall, and when I looked up, I distinctly saw the shadow of an arm and hand reach out to the wall. It was if someone were running and had caught themselves on the wall to duck out of sight from me. I gasped out, and I had my boyfriend check the house for intruders. The back door was still locked and there was nobody there.

That night something happened that had never happened to me before.

I lay down and went to bed. Well I woke up screaming "What is it! What is it! Let go of me!" I distinctly remember seeing a figure at my right, and feeling its grasp on my arms, and a figure at the foot of the bed, pulling me down by my ankle. I was kicking with my right foot to be set free. My head was at my boyfriend's hip region, I was so far down on the bed. When he finally woke up I was still screaming "What is it! What is it!" And he replied "I don't know! I don't know!" and the figures disappeared. He said he didn't see anything, but could tell I was obviously very shaken. He held me in his arms until I fell asleep.
The next morning, while shaving my legs in the shower, I found what appeared to be scratch marks on my left ankle. The ankle that shadowy figure had a hold of. When my boyfriend got home that night, I showed them to him, and it freaked him out. We both thought that it looked like someone had scratched me really hard. We checked the bed and found nothing on or near it that could have possibly made marks like that.

What brings me here today to relate my story, is that something happened again, last night.

I was sleeping soundly, when I woke up for no reason. I saw it was the crack of dawn. I rolled over, and put my arm under my head, and began playing with my sweety's hair, and tried to go back to sleep. All of a sudden I felt this great pressure all over my body. I could hardly move. I couldn't breathe. I tried yelling out to wake up my boyfriend, but nothing would come out. Little by little, I moved my arm, and got my hand to his face. I started pinching it. I thought whatever was happening would stop if I could only wake him up. After what seemed an eternity, he finally woke up, and saw I was in distress and not breathing. He yelled out "Steph! Steph! Are you okay?" I don't remember what happened next but he says I took in a big gasp of air, and fell right back to sleep.
I don't know what is happening here.
I don't know if what is haunting us is even human or not. If anyone has any advice, feel free to email me.
Thanks!