First of all, congratulations on going for your PhD! That's amazing! Many of us here are high-functioning, and your accomplishments make you one of them. Give yourself credit for all you've done thus far. You deserve it!

As an associate degree nurse, I can't advise you on how to proceed with your degree, but brain fog is very common in bipolar disorder. I think it's often a combination of episodes and the meds used to treat them that lead to fuzzy thinking. I had to give up my career because of it. And you're right, Lamictal is one of the major contributors. However, I also agree with your pdoc, you might have ADHD or adult ADD, and there are meds that work well to control that.

Wishing you the very best as you pursue your goals.