Chest pains, dizziness, drastic weight loss.

Hello. I am an 18 year old living in Virginia. I've usually felt like I was in pretty good health. A few minor problems ,but nothing I've ever really worried about until now. Alot of times i'll get a pounding headache and get dizzy like the rooms spinning ,but I never looked into it. Sometimes I'll get a pain in my chest that feels like somethings stabbing into my rib cage on each breath ,but eventually if I can muster up the strength to take a big enough breath it'll start to go away, so again I never looked into it. Recently I started to have pains in the bottom of my stomache that cause me alot of pain ,but like everything else it goes away ,and I try not to worry about it. My heart beats so fast sometimes that I feel like Im going to have a heart attack ,and it happens when I do things that take little to no energy. I didn't really start worrying about it until lately because I've been trying to get over a cold for the last 2 months. The cold has gone away except for the cough. But I started to check my weight reguarlly. I've never been to heavy usually balancing around 140lbs. I stepped on the scale one morning at 132 I haven't been that light since the 8th grade. I stepped on the scale the next day ,and I went down to 128. I have an old scale thats not digital so I know the weight might be off ,but it doesn't explain the fact that I'm still drastically losing weight everyday. I haven't been eating less or exercising more, to tell you the truth I've been trying to put on wieght and eating more ,but I'm still losing weight. Please help.