What Causes Increased Heart Rate When Diagnosed With Anxiety And Shortness Of Breath?

Question: 21 year old male, 57kgs, 172cm tall.
Current medications: Ditropan for hyperhidrosis.
Allergic to penicillin.

Four weeks ago at the gym I noticed my heart rate was reaching 170-180 bmp with very little exercise, a week after that I started feeling short of breath and went to my doctor who diagnosed me with an upper airway infection because I was coughing up milky-sticky mucus (the cough was forced by me and never occurred naturally) and prescribed antibiotics, however the shortness of breath got progressively worse and turned into a choaking like sensation until I ended up in hospital where an ENT doctor told me there was no infection, but he didn't know what was causing my symptoms. Following that my symptoms again got a lot worse, I started having episodes of sharp pain in my left chest that went down into my left forearm, rapid heart rate, muscle cramps in my legs, increased sweating, weakness in my legs and left arm, quite painful headaches that favoured the right side of my head and eye, difficulty taking deep breaths (the notch at the base of my neck inverts more than normal during these episodes), cramping pain that shoots down either side of my neck, a very strong sensation of choaking, feeling faint/lead headed. One episode was bad enough to cause my lips to turn blue and the day prior to that the chest pain was so bad that I thought it was a heart attack, it was one of the worst pains I have ever felt. These episodes are occurring almost everyday now. Two days ago I spent the night in hospital where the doctors preformed many tests on me: ECG, Ultrasound of my heart, CT scan of my chest, blood tests to rule out a clot and cardiac muscle damage, chest and throat x-rays, stress test. In the days prior to that I had an event monitor on for 2 days that recorded the episode where my lips turned blue (although strangely my heart was not racing during this episode and chest pain was minimal). Ultimately however nothing was found and my cardiologist said it is probably just anxiety/hyperventilation. I can't stress enough that I am not suffering from anxiety, prior to all of this I was an extremely happy person but now these episodes are just so crippling that I can't live my normal life, I'm missing Uni and my parents are having to miss work, I think I'm starting to develop depression because of these episodes and having it written of as anxiety is so hard because I know it isn't that, they occur when I'm sleeping, watching TV, on a bus, in a lecture, basically anywhere/anytime. Unfortunately I have no idea what to do anymore. The leading diagnosis from my GP was SVT for roughly a week now due to the symptoms and the fact that ice cold water helped to calm the episodes down however, my cardiologist didn't even mention that. I just really need this solved so I can go back to actually having a life.
I'm currently trying a period without ditropan to see if that helps but so far it hasn't.
Sorry again for the long post and thank you in advance for taking the time to read/answer.

Thank you for responding Dr XXXXXXX Unfortunately I do not have access to my results but I can tell you that there was no underlying pathology with my heart or lungs on any of the scans. I've already had an event monitor on for 48hrs as opposed to the holtor monitor, however I will ask my GP tomorrow about further lung function tests. Recently I've noticed that at night time my body does not automatically regulate breathing well, I usually wake up gasping for air after falling asleep and when I hold my breath I get no desire to exhale or that normal feeling of needing air and it feels like my chest muscles are working harder to support my breathing. Also the neck pain always originates at the back of neck, near the hairline and travels down either side to the anterior aspect of my neck just between my clavicles prior to any of these episodes starting, I'm not sure if that could mean a possible neurological or nerve abnormality for this issue? Thank you again for your support and advice.