My husband thinks I'm stooopid :P?

So maybe it's true that I am, since I've had kids, my brain has been in a fog and I am constantly exhausted. It is affecting my intellect as well. I feel like I have problems learning anything anymore and am having difficulties comprehending a lot of things. Whenever my husband talks to me, I sort of go into 'lala land' and don't feel like getting into profound conversation. We got into an argument today...he admitted that his friend asked him if I was a little slow because I didn't catch some of his jokes. I asked my husband if he felt the same way about me; he didn't say anything. This, of course, lowered my spirits because I always worry about what people think and I believe that what he feels is true. Anyone have any ideas or tips on how to boost my metabolism and brain power...or at least just appear smart to impress him? I am in school for a career diploma, but I feel so exhausted, I don't remember any of it and have difficulty comprehending a lot of it.