The reason why you can't think is because your thyroid and cortisol is messed up.
I spent years struggling through school particularly math wondering why I couldn't seem to get it. I had a recent conversation with a friend about one of my freshman year classes, Euclidean Geometry. The materials make so much more sense now. Heck, it's even kind of fun!
The realization that my ability to learn was so affected by my health problems is mind-blowing. I remember my algebra tutor getting frustrated with me over my inability to hold onto concepts. For years I said, "I love math! It just doesn't like me." And I meant that.