Firstly, I'm so sorry you're dealing with all of that. I'm also young, and during a very stressful episode developed a number of symptoms all in line with what you're experiencing, and it made me feel hopeless, alone, tired, overwhelmed and only acted to compound my anxiety and thus further aggravate my symptoms! It's crazy!
Now, I can say that as much as you feel rushed in and out of the Doctor (I felt the same way), they're *very* well trained professionals with regards to identifying real, systemic problems. Sure, a lot of these diseases include symptoms which one experiences with anxiety, but it's there presence on conjunction with other, major indicators that reveal the real issues. While the internet makes us all feel like we're experts, the articles we read out are no replacement for the countless textbooks, articles, case studies, lab sessions, lectures, and on the job experience that doctors are required to acquire -- remember -- they are actually REALLY smart people who will catch a real problem.
So, firstly, you ARE healthy. I'd bet money on it. Secondly, I really believe your symptoms are anxiety driven, but remember, they're not going to go away overnight. One problem that kept reinforcing my anxiety was that I expected the issues resulting from anxiety to go away the *second* I didn't feel stressed. Unfortunately that's not the reality, as it takes months for your deeper subconscious to really relax, and months for your body to chemically adapt and stop the fight or flight response. I'm a real world, living example -- it took about 3 months of lower stress for my symptoms to *start* to subside. But I can honestly say that they're starting to go away, and I've got such an amazing newfound appreciation for life.
So, ultimately, I'm positive you're going to be fine, do your best to start relaxing, focus on doing things you love, drink tea, read, play video games -- whatever it is -- don't be afraid to focus on yourself and lastly, don't lose hope -- you ARE going to get better and you ARE going to have an amazing life!