I am honestly completely out of ideas as to what could/is wrong with me. I think it may be some sort of a learning disability, but i really don't know. I'll explain

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I'm 18 years old, and I barely passed through high school and I'm almost finished with my first year in college. I remember all throughout my school-years every teacher telling me that i just need to "be a sponge, don't let things just go in one ear and out the other. Suck everything in and keep it in your mind." But I can't. My parents were always telling me that I'm so much smarter then I prove myself to be, which is true, but I just can't do anything about it.
No matter how much I study for a test, or for anything for that matter, I can't remember <i>anything</i>. Literally. For instance, I have no idea what my professor talked about in class today, even though i remember paying attention and taking notes. I could make notecards, and study them everyday until the day of a test and i still wouldn't have any idea what kind of bone marrow is in spongy bone. Or what Freud did for the world of psychology. I have never aced a test. i have never passed a test.
I have tried everything, even different ways of studying, and not even studying at all, or studying less, in case i was just overloading my brain. Nothing helps.
And it's not just tests. I can't remember anything. No matter how much i try to pay attention, i can't ever get my brain to focus on what's going on, at all. My brain is always going, thinking about other things. What other things? I have no freaking idea. It's like my brain goes so fast, if you asked me what i was thinking about, i wouldn't be able to tell you because the thought passed so quickly. That's the easiest way i can explain it.
For instance, if my fiance is driving us somewhere but he needs to get something in the backseat and we're at a stoplight, he'll ask me to let him know when the light turns green. I can't even do that. No mattter how much i want to remember what I'm supposed to tell him, i just can't. I can't stay focused.
I suppose what made me snap was i tried to get my permit yesterday(which i had been postponing for a while because I was trying to know the stuff before i took the test, plus i was nervous about the test in the first place) and before i took it, i was in the waiting room and i was reading directly from the book, eeverything i needed to know. And i walk into the room, confidantly, and start to take the test, and i can't remember Anything.
bottom line, I failed the test horribly.
it just made me snap.
I'm so tired of barely passing everything! of not making it through. Of failing. And I need to know what it is that's making me like this because once I know i can learn more about it and try to fix it.
someone, please help me.