It's not a learning disorder.
You need to learn how to analyse - lots of tips in this thread already.
I find a lot of my undergrads have big ideas, but can't give me the step-by-step logical argument to support their thinking. You need to have evidence. Depending on your subject, your evidence will often come from your work in interpreting the primary source materials you engage with.
First of all, work out what the essay question is really asking. Then assemble your relevant primary sources.
So if you're reading EngLit or History or Art or .... , start with a book/text/primary source/document. Work through it, understanding it's implications, its connotations, its sub-texts, its figures of sppech, its visual tropes (as appropriate). Do a 'close reading' or a 'thick description.'
Think about how that text (of whatever sort) produces meaning and how you might interpret that.
Then think about where/how that text is situated in its cultural/historical/social context. What is its significance? What is the cultural work it does?
That tip of writing points on papers after reading is really useful too whododat because I get very overwhelmed with a high volume of highlighted sheets of paper and books with sticky labels sticking out. Is it the same principle for a chapter of a book too?
Thinking & learning & writing (writing is a form of thinking & learning) aren't about collecting "quotes" they're not quotes they're quotations and lining them up.
You need to engage with the central argument or idea driving what other scholars have written.
But the FIRST and most important thing is that you need to have your own driving argument, drawn from your analysis of the primary sources.