Welcome to Just Answer and thanks for your question. What evaluations have been done so far? What medications/drugs/supplements are taken regularly?
Do you have the numerical results of the high white count? I'm looking for how "high" is "high?" Do you have the differential results (basophils, eosinophils, neutrophils, etc.)?
White blood cell count is up in the face of any type of infection. Since your doctor said "not too high" I am assuming this was the reason. The rest of your symptoms are so diverse that it would prompt a provider to check to see if you might have a lot of stress and anxiety that is at the basis of your symptoms.
Your doctor could readily test for Lyme disease. About 80% develop a characteristic rash that can spread to be as much as a foot in diameter within the first month after a tick bite. There are many false positives in ELISA antibody tests, so if it were positive your doctor should order a Western Blot for confirmation.
You mention a therapist. Was this a psychologist or a psychiatrist and did you take/are you taking medication for PTSD?
I'm glad to hear that you are doing so well with the PTSD. It would still not hurt to talk to a physician (psychiatrist) about the possibility of an anxiety disorder. You really have nothing to lose at this point, unless your primary doctor can come up with some physical explanation for symptoms that affect the muscular, digestive, skeletal, respiratory, cardiac, and neurological systems all at the same or similar time frames. Your mention of "...Frequent spells of "fluttering" heart, internal jitteriness, internal tremor" are classic anxiety disorder.
There are few diseases that can affect all body systems at once. Lyme disease, lupus, and early MS are the big ones.
Congratulations on furthering your schooling. What they may not teach you in school is that not every panic attack is the same, and neither is every anxiety disorder, even in the same person. Just as two headaches or two pregnancies are not necessarily alike. So saying you've had panic attacks and anxiety before and would recognize either doesn't necessarily mean anything. I hope you will consider the psychiatrist if the ID doc finds nothing.