Hi My Name Is Nick, And I Was Put On

Hi my Name is Nick, and I was put on beta blockers a few months ago for some reason as of lately, there are times it makes me really weak,confused and feel cold and like I am going to pass out. I was put on them due to my heart beating to fast, which caused my breathing to be more shallow meaning I could not ever take a full breath. It has been better since the medication, but now I have tightness not only in my chest, but its now also in my upper stomach, right below my chest. Even on the medication there are times when It is almost impossible to take a full breath because of the tightness.