17 y/o girl. recently been bruising a lot easier on arms and legs, i've been getting itchiness on arms and legs causing petechiae, doctors? causes?

Easy bruising: Easy bruising can be seen in some serious illnesses which cause a decrease in the number of platelets. Seen your doctor for an evaluation.

See a doctor ASAP : With the easy bruising and petechiae best would be to see a pediatrician / internist / hematologist to have a work up to determine the cause.

Mgt and workup: When you see your physician, you can provide them with a medication list, and ask about having bloodwork including a CBC, differential, platelets, coagulation studies and liver function testing.