I see a serious potential drug interaction which you need to be aware of:

Zoloft and methadone:
http://www.drugs.com/interactions-ch...78-0,2057-1348

One has to be VERY careful with methadone!
Here is why:
http://neurotalk.psychcentral.com/post15298-4.html

Methadone is a long acting, drug. When the body cannot clear it well, it can build up. It will remain in the body, after leaving the pain receptors, and patients then take more, and this leads to overdosage, CNS depression, and breathing risk.

It can also affect the heart rhythm and lead to sudden death that way.
http://www.azcert.org/medical-pros/d...-drug-list.cfm
http://www.azcert.org/medical-pros/d...-drug-list.cfm

New warnings:
http://neurotalk.psychcentral.com/thread172712.html
Methadone overdose can come from patients increasing their own doses, or by taking other drugs, that impair the metabolism of methadone.

At age 50 there can be impaired glucose metabolism. You can help yourself in this area by avoiding sugar and starchy carbs.
Limit them at every meal. Instead choose lean protein, and fruit and veggies. This can stabilize blood sugar swings, and help with the brain fog, tiredness, visual blurring.
But you really need to get evaluated for diabetes, have an A1C level drawn, to be sure. Undiagnosed diabetes will impair kidney functions, and affect drug clearance rates as well.

So I really urge you to see a doctor and get that screened.