When a 31 year old start getting ptosis in there left eye and then moves to there right eye months later.. is that a sure sign of myasthenia gravis? or could it be something more simple?

I would consider this to be myasthenia gravis until proven otherwise A neurologist is best to consult for diagnosis, appropriate testing and treatment.

This is a suspicious presentation for a neuromuscular disorder but is not clearly pathognomonic for myasthenia alone. Would certainly see an ophthalmologist to rule out ocular myasthenia, and consider neurologist next.