If you just started taking Adderall (XR I am assuming??), then your doctor, like most others, probably started you out at a very low dose such as 10mg. The purpose of this is to slowly acquaint your system with the medication, as well as to intend to increase the dosage because each person is different and may require different dosages.
If you doctor did not tell you to increase your dosage in 1, 2, 3 etc. weeks, then you should probably contact him/her and let him/her know you need to increase your dosage.