I have low energy, but don't want to rely on caffeine or other stimulants. Any suggestions?

Sleep. The first step to having more energy is to make sure you are getting plenty of sleep. A balanced diet, staying hydrated and getting plenty of exercise can also increase your energy level without needing caffeine.
Cover your bases. Low energy can be a symptom for hypothyroidism, depression, anemia or sleep disorder. The first thing is to make sure you are getting good sleep and practicing good sleep hygiene, which is going to bed at the same time, getting up at the same time, using the bedroom for only sleeping, changing clothes and sexual activity. There are other parts as well. If this doesn't work, seek a doctor.