Have been taking Lexapro (escitalopram) daily (~1 year), but last 2 mos feeling drowsy/lethargic. Related?

Could be. May not be related but there is an "a motivational syndrome" that sometimes occurs after prolonged use of ssris.
Doctor can evaluate. A person on a drug for 10 months at the same dose, and then starts to have drowsiness that persists, should see the doctor for re-evaluation. Maybe the medicine has gradually affected the person's blood count or chemistry. Maybe the patient began a new medicine, supplement, diet, etc... Depression comes and goes; maybe different dosing is needed. Maybe symptoms have nothing to do with the lexapro (escitalopram).