The stimulants prescribed for my ADHD don't seem to be working. What should I do?

Re-visit diagnosis. It's extremely rare for stimulants to not work in adhd. If adequate dosages have been tried, i would recommend discussing with your doctor whether any other diagnosis would explain symptoms that seem like adhd but perhaps aren't.
Schedule appointment. The best thing to do here is to check in with your prescribing physician, and be as clear as possible with him or her about the progression or your symptoms since you've been on your current med regimen.
ADHD & MEDS. More information is needed.So is a reassessment.Were the meds working and now they are not? Are there any new stressors in your life? Recent illness? Sleep problems? Are you taking any meds or alternative therapies that you were not taking before?...See your doc , more information is needed.
Let your doc know. Soetimes knowing if the meds r working or not is subjective - sometimes it is simply a matter of dose - the effectiveness of the stimulants and actually which adhd and cognitive symptoms they best address are dependent on their level in the blood. At other times there are co-existing orders that may also need to be treated. If meds dont seem to work, its always something 2 talk to ur doc about.