I haven't had bad of an experience taking tests, though I too always did pretty bad on most tests, though knew the subject, and did fine on everything else.
Is there any way you can see a different advisor? It sounds like your advisor isn't really all that keen on really helping you succeed. Maybe you can take it to a higher person, let them know whats going on. I would definitely say go and see a psychiatrist, as they have more power and weight to be able to verify that you really do have an issue, and in addition to helping you maybe deal with it better, can also give notes etc, to the advisor, or teacher, and come up with a solution that works. I can't imagine what you have to go through every time you have to take a test. Hopefully a psychiatrist can help with minimal or no drugs, and you can succeed in college.
Just another idea, what about online classes? Sometimes they have fewer tests, and maybe being able to take the test online at home as opposed to going into the school to take a test may help a little? Just throwing ideas out there. I know for me I still sucked at tests, but it was easier taking them at home on my own time, and not being in the classroom with everything quiet, and judging how I'm doing based on when other people are done. It was much easier being home, listening to music, and being in a comfortable place. Wish I could be more help.