A lot of it is lack of sleep.
Even if you think you are sleeping well, when you are in early recovery (when does it become late recovery? ha!) your sleep cycles are disturbed. When you do sleep, you don't enter the deep, restorative sleep below REM sleep. REM sleep is where you dream, so you might notice you recall your dreams more now, too, at least for awhile after you wake up. You don't remember dreams from deep, restorative sleep because you don't dream then. In normal sleep, you go in and out of those sleep states all night. In recovery, you are lucky if you get a few hours just of REM sleep.
Without good sleep, you will feel tired and mentally dysfunctional. Sleep medications can make it worse, because you don't get the deep sleep. Same thing for alcohol, which also disturbs the sleep cycles.
When does it get better? For me, I finally started getting more mentally clear after about 3 or 4 weeks. It's different for everyone. I have a job that requires a great deal of mental clarity, and I've muddled through while getting better. After about 3 months, I realized I was thinking far more clearly than I ever did on opiates, even though while using I truly believed I was doing "my best work". HA!
Give it time. You are still healing.
FT