It may be the Risperdal, Lithium for many, doesn't do that, if anything, you'd find functioning more improved than when you weren't taking it.
You may also want to have your thyroid function checked out, cause sometimes Lithium can cause hypothyroidism, which can make one feel fatigued,foggy, and many other things. Regardless, Lithium is a great med., if you need to take thyroid meds along with it, that is not a problem.
I wish you luck with this, don't get discouraged, it takes time, but getting the right med and dosage(s) can make a huge difference.
Take care,
DE

BTW
It is a good idea to contact your pdoc or who the prescribing physician is, meds can effect people differently, plus the disorder can cause various changes, so it would be best you ask the doc about your meds and how they may be effecting you.