I've been suffering from POIS since 2000, posting on POIS forums since 2009 (Naked Scientist Forum) and more recently on here (since 2011), and I've finally found something that has consistently worked for me.
For the last 6 weeks, I've been taking milnacipran (Savella) before O. After O, there has been no brain fog - every time. My physical symptoms (dry hair, dry forehead, clicking knees) have also gone.
The milnacipran has an unusual side-effect - my Os feel much more intense, and last much longer. This hasn't happened with any other medicines I have tried, and I have tested many different medicines over the years. Again, this happens every time.
I have been taking one dose of 25mg approximately 1 to 1.5 hours before O. Initially I combined it with fenugreek, but now I take it on its own. The result has been 0% brain fog every time.
Milnacipran is an SNRI that inhibits norepinephrine reuptake even at low doses - other popular SNRIs venlafaxine and duloxetine (which I have tried) need much higher doses before there is any significant inhibition of norepinephrine reuptake. I believe that it is the norepinephrine action of milnacipran which is somehow preventing my post-O brain fog.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2938282/It is early days now, but I sincerely hope that milnacipran will continue to work for me in the long-term. If it becomes less effective or stops working, I will come back to this thread and update it.
I would be happy to answer any questions.