Can something systemic cause an increase the amount of cavities i get? major increase in cavities the last year but haven't changed any oral habits.

Possible diabetes: a rapid increase in caries may be related to higher glucose levels (glucose is sugar, it is in the blood and saliva), I suggest that you get checked for diabetes. If you already know that you have diabetes consider checking for better blood sugar control

Dry Mouth: A dry mouth can increase the incidence of caries.

At your age....: it's unlikely but yes possible and therefore it should be checked out by your own physician. More than likely something has changed although you might not be aware of it. I once had a 13 year old patient who almost never had a cavity. On her regular checkup one time she had 13! Mom said nothing changed. We discovered she started having fruit roll-ups all the time. That's concentrated sticky sugar!