I don't know that I would call it an overdose. Sounds like it was taken longer than intended. Methylprednisolone is a steroid. It should NOT be stopped abruptly after four months or there will be w/d symptoms. You really should be seeing a dr about this.
Read the following link. This will give you what information I have for methylprednisolone.
I am not a dr. My statements are based on years of experience and related education. Consult with the professional of your choice regarding matters of concern.