I'm a 20 year old kid who's keeps up with his brushing but still white under my teeth is still forming, what should i do. they said i brush to hard, should i see a doctor for a prescription?

Get a cleaning: you cant brush away the calculus or tarter that collects on many peoples' teeth. Your dentist or a dental hygienist who works with him /her will get that off for you. You should schedule regular visits to keep your gums healthy. Don't brush too hard or you will damage your teeth and gums. Use a soft or medium brush and change it frequently.

Rotary toothbrush: Use a dental regimen of brushing at a 45 degree angle between the tooth and gingiva and using dental floss religiously to avoid gum disease. The white you describe may be plaque buildup. It may be helpful to use a rotary toothbrush if you feel that you are not able to adequately manage with a manual toothbrush.