According to your negative ECG-report and data about having a stressful life, your chest pressure could be stress related. Stress is often manifested with symptoms of a real organic disorder.

Do you feel burning sensations behind the sternum? That could suggest acid reflux.

You could have acid reflux, so you could take a natural remedy or OTC remedy, or even talk to your doctor about taking a prescription. When I was pregnant, OTC prilosec helped me a lot. If the problem doesn't clear up for you in the couple weeks as it indicates, it's either not going to help you or acid reflux isn't your problem. If it does help, you can continue to take it, even though it says you aren't supposed to: that is just supposed to protect people from taking it when they actually are taking it to cure acid reflux when their problem is actually heart disease.

If all this is from anxiety and stress, that makes sense too. You can post in the anxiety/stress disorder section and will find much help there too