Foggy-headness, trouble concentrating.

The same thing happens to me sometimes! I don't think that this inability to concentrate means that you need to take medication - this sounds fairly normal!
It sounds to me like you are under a lot of stress right now. You say you've been a great student for a long time - simply making great grades in school can really do a number on your stress levels!
When your brain and your emotions work really hard for a long period of time, you can start to get 'burned out' which can lead to the foggy-head feeling you're talking about! The effects of long-term high stress can be felt physically and emotionally, as a signal to tell you to 'slow down' a little bit. Try to do something relaxing every day, like going for nature walks, drinking herbal tea, listening to zen meditation music, or doing simple yoga (there are lots of "beginner's yoga" instruction videos on youtube. I've personally used them and found them very relaxing!).
You may also find it helpful to talk to someone. Your college probably has counselling services - try asking at your school's student resource center. This may be new to you but I promise that simply talking about what's bothering you can really help ease your mind.
Try not to worry too much about the foggy-headedness. It will pass in time as long as you keep being good to yourself! It's good to hear that you take supplements and sleep well, but try to give yourself some more 'me time'. Talk to someone if you're comfortable. And if you ever start to get really scared, just take a deep breath and remember "this too shall pass". :)