Well, a pineal cyst is common and normally causes no problems, EXCEPT when it occasionally becomes too large, upon which a whole raft of symptoms will visit on a person, including your headaches and things like vision trouble. Also, sometimes it can push on parts of the brain, which MAY be causing some of your other problems, altho I'm not certain. Therefore, since it's been a while since they did the MRI, I think you should have another, to see if that thing has gotten larger than before.
I'm glad you have medicine for your headaches. But now you have pain when walking, weakness on the left side, and apparently untreated seizures. These strike me as neuromuscular type problems, whether from the cyst or some other cause, and a neurologist needs to reevaluate you, and he MUST give medications to treat those, it's especially not good to have seizures. He may trace those back to the pineal cyst, or he may uncover yet another problem, the latter of which is more likely. Those would be my thoughts.