Since lexapro dosage has been increased, i've had increased anxiety, feeling overall horrible, and eye twitching. could it be serotonin syndrome?

Maybe, but: it sounds like side effects of the medication if everything else has been eliminated. Make an appointment with your prescribing MD right away. If you can't do that, go to an Urgent Care facility, and as a last resort, leave a message with your MD telling him/her your symptoms and ask that s/he leave you voice mail instructions in the interim.