Sometimes I Get Numbness In The Left Shoulder Blade, Please Suggest Me

Hi, I am 19 years old and very active (tennis, swimming, etc.) and I had chest pain about 3 months ago and had an ECG done and nothing wrong was found. Then the pain went away for a while. About 2 months ago I felt numbness on the left side of the chest and I thought it was anxiety so I did nothing about it and it went away. Recently, it feels like there is some tightness around the left part of the chest and I sometimes get numbness in the left shoulder blade. I also get shortness of breath sometimes and some pain on the left side of the chest and on the left arm. I think I worry myself way too much and might be causing these symptoms thinking it is a heart attack. Still to be sure I have an ECG tomorrow. Do you think I have anything to worry about? Thanks! Also, I don t feel worse when I exercise, I actually feel better sometimes which also seems to point this is anxiety caused. Update: Had an ECG today and everything was normal. What could this otherwise be ? Thanks!