Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor. Without the ability to examine and obtain a history, I cannot tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
I am sorry to hear about all the medical problems that you are experiencing. I am going to try to focus on your difficulties with concentration, and memory as these seem to be your primary concern right now. You mention a history of thyroidectomy, and one differential to consider is hypothyroidism. Low thyroid function can cause fatigue, weight gain, cold intolerance, constipation, and memory/concentration problems. You should have your thyroid levels checked to ensure that you are being adequately treated. Another possibility is anemia, which can cause severe fatigue and thinking trouble. In addition, other causes include certain vitamin deficiencies. These can all be diagnosed with simple blood tests.
Another group of problems that can cause thinking problems and fatigue are psychiatric. Clinical (medical) depression and anxiety can sometimes be expressed in this way. Also, attention deficit disorder (ADD) may sometimes be the cause of concentration and memory difficulties. Many people think of this as a childhood disorder but it can start in childhood and not be diagnosed until adulthood.
A less likely possibility in the absence of other neurological symptoms is that there is a brain lesion that is causing your memory/concentration issues. I am using a very general term in brain lesion, as there can be many different causes of lesions in the brain including autoimmune, malignancy, vascular, or infectious. If your symptoms are occurring episodically, another possibility to consider is seizure episodes. Seizures can present as confusion or memory loss, and do not necessarily need to have motor involvement.
I would recommend seeking an evaluation with a neurologist. Based on the clinical exam, an historical findings, your neurologist may recommend further work-up that may include bloodwork, MRI of the brain, and EEG.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
I am no doctor.. but a lady that has been through tons of workups over the years trying to explain symptoms. Have you been seen by a neurologist and Rheumatologist? Seems to me you might have some sort of autoimmuine thing going on. Also.. word of advice.. get copies of your medical record. I had found out my problems were documented with a diagnosis.. needing surgery.. they didn't tell me. Not wanting to pay for expensive surgery...I had to change HMO to get treatment...very wrong. Hope you get answers. Hope you feel better soon!