Why am I getting light headed all the time?

Many reasons. 25 year old could have dehydration, pregnancy, migraine, low blood pressure, stress, diabetis mellitus ... To name a few. Get a check up with your primary doctor.
Many reasons. Hypoglycemia , low blood pressure are very common possibilities.I suggest a good physical exam!
Light Headed. One of the most common causes of light-headedness is dehydration. Increase your clear fluid intake, ie-water, juice, gatorade or kool-aid, and see if your symptoms resolve. If not, see your primary care physician.