The feeling that you have is completely normal this early in sobriety. After the acute withdrawal is over, there is something called PAWS (Post Acute Withdrawal) that we all exeprience. Your brain is in the healing process right now - while you were using, the opiates took the place of natural endorphins and neurotransmitters in your brain, so your brain did not need to produce its own. Now that you are clean, your body is learning how to produce these once again and as your brain heals, it will learn to use them again. It typically takes 90 days for your body to use your own endorphins the right way. PAWS is something that can last up to a year following detox, but it is not present every day, the worst symptoms hit at around 30 day cycles typically. With me, I typically feel tired and brain dead, I cannot concentrate and the worst is when people tell me something and 20 minutes later I can't remember it. It will get better. There is some great imfornation contained in the Health Pages on PAWS. Keep moving forward and keep posting for support. Take Care
Welcome to the world of recovery. I have several months, and I have days like that occasionally. Be kind to yourself...this too shall pass.