Pa. has decided I need a Medical Review in order to keep driving?

I am a senior citizen, who is dyslexic and also has degenerative disk disease of the spine. I have never had a traffic ticket nor ever caused an accident. I only live in this area of Pa. having relocated from another 3 months ago. I was stopped by a cop for changing lanes too often. Here, we have to stay to the right to go to a right hand store, left for the same, middle for no change. I did not know where a store was so had to legally <I thought> change lanes while trying to find a place. I signalled each time. A cop pulled me over and told me I looked like I was lost. I said I was and instead of letting that go since changing lanes is legal, he asked me why I had on a cervical collar. I told him my health problem and he asked what kind of medication I was on at that time. I told him I only took medication at night. He claimed once again that I looked lost. I was lost. Now Sat. I got a letter from the DMV stating that it has been brought to their attention that I have a medical condition and I need to have my doctor fill out a form stating how long I have been treated for this, what meds I am on, how often I take them, how does this affect my driving, etc. I have dyslexia and was not on any medication but do not even have a doctor here yet. I take mild medication only at night although I was prescribed by my doctor in my prior area of Pa. to take as needed. He is now gone from the area. How am I suppose to prove a negative. I have a safe driving record and unfortunately dyslexia. I have no problem reading only directional issues. They will take away my driving privileges and I can only walk with a cane. Help, please.