Is what you are experiencing, the jinn's possession, considered a psychological illness?

The existence of jinn is affirmed by the consensus of the early generations of the Ummah, and by the Qur'an and Sunnah. The entry of a jinn into a human body is also affirmed by the consensus of the imams of Ahlus-Sunnah wal-Jama'ah, just as Satan flows through the son of Adam like blood and flees upon hearing the Word of Allah.

It is recommended to recite the Qur'an, remember Allah (dhikr), seek forgiveness (istighfar), and resort to Allah through supplication (du'a). There is no harm in going to a shaykh known for his righteousness and adherence to the Sunnah to recite ruqyah ash-shar'iyyah.