I get a good amount of sleep each night normally, I do excersize during the day and eat healthily - why am I always so tired?

Depends. I don't know your age or overall health, but it seems you are basically healthy. There are a few things you should consider. One, is a test for your thyroid funciton. A simple blood test could give you the answer. Medications? These can do the same. Do you snore? Sleep apnea can be insidious! I would suggest a good check up, some labs and hopefully some reassurance and continue exercising.