I am 25 and my hands tremble very bad. I don't even notice it anymore but people around me do. What could cause this?

Many causes. See a neurologist or your doctor to make exact diagnosis.
Get it checked. You may have a thyroid problem. Hyperthyroidism, to be exact. Tremor is a common symptom. Along with heart palpitations, intolerance to heat, and eyes that appear to be bulging; to name a few. See your doctor. If truly hyperthyroid disease. It should not be left untreated.