OK, let's start with
Autism :
the inability to focus during study is a major problem in teenagers with mild-moderate autism , some of these difficulties are manageable with the use of some psycostimulants with a lot of effort in study during the time of action of the drug , vyvans is a famous psycostimulant which is used in
ADHD patients who can't focus , it has a half life of 10-13 hours which is long enough to make some academic achievement . the starting dose is 20 mg and can be increased weakly by 10 mg to achieve its full potential, max dose is 60 .
the second question is related to
polyuria, which is must be investigated , although in people who take multivitamins it's common to have some polyurethane
the investigations I suggest are :
urine specific gravity , urine spot for sodium and
creatinine , urine osmolality , serum sodium and osmolality. fasting blood sugar .
you should always look for psycogenic polydypsia which is consuming huge amount of water that results in polyurina , it's common in children with autism .
I hope this helps