Hi msnow -
Since medications affect different people in different ways, I can't tell you how long Buspar will make you feel tired, or even if it is the Buspar which is making you tired today.
Sometimes it takes some trial and error to find the right med, or combo of meds, that make us feel the best. You and your doctor are the treatment team in this process. Please let your doctor know what is happening, and follow his/her advice.
We can share our own experiences, but the only one who should tell you whether or not to stay on a medication is your doctor.