For the past two days, my chest has felt tighter than usual. It sometimes feels like I'm not getting enough oxygen. My upper back also feels sore when this is going on at times. My heart will even start beating fast like I just ran a marathon at random times.   I'm 15 + 4 days and I've read some places that it's normal and other places where a dr visit is needed. I worry over everything and have even read about it being a possibility of a blood clot. Any advice or personal experience on how to make this go away?