Hi there! How old is your son? The reason for asking that is sometimes those meds don't work as well with teens and pre-teens. As well, we have a community specifically for youngsters and family. The weight gain is because it gives more impulses to eat, it doesn't just pack on the pounds by itself. So you may have to be more vigilant with his diet. I would certainly go into his psychiatrist and talk about this new problem and get it addressed as soon as possible.
ive been on it for a year also, and just recently have been having the same side effects. ive had terrible nightmares that effect my sleep and my ability to function all together. i wish i knew what was wrong and could help- whenever i talk to my doctor she just ups my dose and tells me to give it more time. im now taking 40mg of fluextine (prozac). the other meds have worse side effects though, such as wieght gain- which for teenagers can be a big deal. make sure you research yourself before switching, and please keep me posted. i wish your son the best! i know what he's going through- it's a really rough time! if he wants someone to talk to his age, i am17 and in the same situation.