Agreed - methylation issues, pyroluria, ADHD, etc etc can all easily contribute to symptoms you describe.
If you've had no trauma and nothing particularly bothering you - you've gone down the therapist and oral antixylotic route - it's worth DNA testing.
Also the urine test for kryptopyrolles is worth persuing too.
GAD gene converts glutamate to GABA - GABA is the neurotransmitter which is INHIBITORY - calms us down..stops mind-racing...etc.
Within the 'YASKO Methylation Cycle' diagram - genes such as GAD, MAOA and MAOB, SOD, CBS, MTHFR, COMT, VDR, NOS are all the important ones which affect very important enzymatic conversions. When these genes are mutated, half-mutated or fully...that conversion is challenged...mostly the effect is under functioning of that gene, but at times, like with the CBS gene (which creates ammonia, which is neurotoxic, triggers fight flight and thus anxiety) the action of the enzyme can be working up to 10 times as much as normal. 10 times as much ammonia as normal is an extreme stress on the body and will, eventually cause symptoms.
So the gene route is worth persuing...it helps you to see within the methylation cycle which genes are mutated and with further research (on yasko's site, she has a free book for download or pheonix rising forum (gene testing section of their forum), NOT CZ as the mods wouldn't start a forum for nutrigenomics as i requested so you're better off going to other Health Forums
for learning more on this angle of health protocols.)
Aside from that i would also recommend doing a hormone panel of tests. Saliva is generally preferred, altho' mainstream MD's use serum which shown bound as well as unbound hormones, a useless number as unbound 'free' hormone numbers are the 'active' hormones, bound hormones (to proteins and other things) are inactive...so numbers are useless.
Canaryclub.org offer the cheapest (that ive found so far) saliva testing online for you to self-order. Excellent site - well worth joining.(They do male and female comprehensive hormone panels)
I'm not sure if you're male or female, but certainly hormones are worth checking out. Low testosterone creates a feeling of lack of self-esteem and confidence, which can translate quickly to anxiety as we don't feel as confident as we really are. Anything that makes us feel unsure about ourselves creates anxiety. Hormones have a great way when unbalanced of making us feel unsure of ourselves!
Pregnenolone is a natural anti-anxiety hormone - it's a master hormone which makes all others like estrogen, progesterone, testosterone and cortisol. If you're low in pregnenolone and are stressed (from starting college?) you're body will shunt making other hormones in favour of producing cortisol to handle the extra stress you're feeling, resulting in lower than optimal testosterone etc etc...which WILL affect mood and change how you feel.
Diet clean-up and improving your gut health are other paths to do down too if you've not already been there.
We make the majority of Serotonin in our guts so if you have bowel problems that can be affected.
As well as of course absorption of vitamins is compromised with bad bowel health thus causing lack of nutrients getting to your cells to do their jobs...leading to physical/mental changes over time.
I know what crippling anxiety is like and i wish someone had told me this stuff 10 yrs ago! I really hope it helps...it might sound a lot to take on..maybe confusing...but whatever you do - only go on benzo's and psych meds if NONE of the above helps you.
Huge luck to you :-)