Hey, yeah, definitely could be PTSD. I had a major breakdown and went from uni and two jobs to not being able to be asked a question like "what do you want on your toast?" without panic.
So, severity-wise, it's totally in line with a PTSD diagnosis.
That being said, if you drop your doses of anything, or take anything new, that can also make you freak out. A lot of people have PTSD and anxiety, or PTSD and panic disorder, or PTSD and depression too.
The other thing that's possibly going on is it might not feel like the doctors are listening to you because they say "It's normal", and I'm sure it doesn't feel normal. Doctors are exceedingly strange creatures, to whom "normal" means more like, "expected", or "fits with the diagnosis and isn't going to kill you." I've banged on about that in other posts, but literally if it's expected, they've got an extremely flexible definition of what "normal" is. (Source: I grew up with 2).
Secondly, you mentioned you were interested in how PTSD works in the brain. It's kinda an interest of mine, I used to be an EEG tech, so I'll give a brief explanation if you're interested.
PTSD changes the structure of your brain. Literally changes it. The change is reversible, but not without work. Compared to a typical brain, our amygdalas and survival brains are larger. These are the prehistoric elements of our brains, that we share with lizards etc, so I call them "lizard brain." They deal with the four Fs, fighting, fleeing, feeding and.... mating. The amygdala governs the first two, and ours are disproportionately large generally speaking. Check out some MRIs of PTSD brain on Google if you like, it's fascinating.
The bit of our brain that shrinks to make room for this is called the hippocampus - hippo meaning horse, kampos meaning monster - so named because it's seahorse-shaped and in the middle of our brains. This is the bit that governs the "where/when" function. This is especially relevant when we're triggered. The hippocampus is offline, so we perceive that the danger from the memory is in the here-and-now, instead of the there-and-then, so the rest of our brain reacts like the danger of the trigger is the danger in the memory. Explains why we freak out so badly physically, and emotionally.
Lastly, our sensory organs are a) hyperactive because we're in danger mode and b) generally wired straight to the lizard brain through reinforcing that during trauma. The brain is made up of neurons, and when these activate, they build pathways. They connect to each other and "wire" the ways they think they're supposed to work. Trauma reinforces our sensory organs should connect to our "danger" mode.
We develop extreme sensitivity to stimuli because our brain is trying to keep us safe.
Everyone has good ideas for strategies with that, and this post is long enough already. If you're interested in more science I'm happy to share what I know, but I'm not a doctor and don't know everything.