Yo dayglo,

It might also be as simple as needing a higher dose of Ritalin - I take 40mg a day (in four doses) and sometimes an extra dose when I'm staying up late doing an assignment. The recommended maximum dose is 60mg/day and doses can be up to 20mg each. So it might be worth thinking about.

And yeah, the serotonin thing is worth investigating. It is also possible to take a serotonin drug AND a stimulant (I do!! My psychiatrist and I pondered for a while over whether Efexor (which also affects noradrenalin/epinephrine) and Ritalin was safe and couldn't find anything to say I'd die from the combination... so far so good )

Also down on the ADHD/ADD board further down the page there is a lot of talk about different drug options and also non drug stuff which is definitely worth a read.