Anxiety symptoms can definitely get to the point of being relentless, 24/7 and frightening. I had a lot of those tests done too, when I was about your age and running around trying to get help, the EKG, the blood tests, audiology. And all I ever got out of those was, "There's nothing wrong with you; it's all in your head." My family's reaction to my panic attacks was always, "What are you DOING to yourself?" and even once, "Are you on drugs?"
I give you a lot of credit for taking trips and maintaining a social life. Truly, that's difficult. There are a lot of things that can help, and I hope you find some activities like that soon. For me, one thing that helped was sitting down and writing a longhand letter to a friend explaining what was happening and how I felt...I never sent the letters; they were more like the journal that some people keep of their anxiety problems. A lot of positive self-talk, and one of the weirder things that helped, and still helps, is watching baseball games. That bores some people, but it's not a fast violent game, and there are a lot of details in a game that divert me from the anxiety.
Keep reading about it, and talking to other people with anxiety problems. It's so treatable if you just find the ways of coping that work best for you.