Changed ssri dose a week ago. nauseous, tremor, low grade fever, feeling kind of out of it. had serotonin syndrome before. could this be that again?

Yes, serotonin syn: If can be if you had it before. It could also be a cold. Serotonin syndrome is unlikely if the med dose is in the recommended range unless you are on other meds that interact or have a metabolism problem. There is genomic testing that i'd advise to see if you have a metabolic problem that might guide dosage and med.

WBC elevation?: I would not be so fast to blame these symptoms on the change in your ssri as they are rather 'classic' for infection of some kind, viral or bacterial. It is wise to give the feedback to your prescribing doctor on a weekly basis when starting or changing an ssri as a few individual can plummet into suicidal ideation. There's no harm in holding your dose while you go for a physical exam and labs!

Serotonin Syndrome: For diagnosis of serotonin syndrome, at least three of the following signs or symptoms are required: •agitation •diarrhea •heavy sweating not due to activity •fever • confusion or hypomania •muscle spasms •overactive reflexes •shivering •tremor •uncoordinated movements your symptoms do not seem to indicate serotonin syndrome. Due to past history, please see your psychiatrist.