Botox and side effects
Botox around the eyes will correct fine lines and crow's feet. However, Botox will only last up to 4 months in that area. The facial twitching that you are describing from Botox is not from injections 20 months ago. I would consult a neuro-opthalmologist to examine the cause of your symptoms.
Botox wears off
It is unlikely that you see any effects from having Botox 20 months ago. You should discuss with your primary care physician about your new twitching.
Botox lasts 3-4 months
Botox wouldn't last as long as 20 months. It wore off long ago, and you're just noticing some eye twitching that is unrelated.
Eyelid twitching and botox
It is unlikely botox could cause that type of damage to your eyelid muscles. In fact, botox is often used to reduce eyelid twitching called blepharospasm since it prevents the transmission of nerve signals. Fatigue, injury, stress, etc. can all be causes of this condition. Botox as I said is often an effective treatment for eyelid twitching.
Lids can twitch for a variety of reasons
but its certainly not related to your Botox as your Botox is long gone from your system. If you have major issues with twitching, see a local physician to get evaluated as you could have spasms that may need Botox for treatment.