You are using the NPN as a saturated switch. To properly turn on the NPN, its base current should be ~Ic/10, so one tenth of the motor current. If your motor current were 0.2A (my guess), the base current should be 20mA.
Assuming that the PIC can pull up to +5 at 20ma (which it cant quite do), Rb would have to be (Vdd-Vbe)/Ib = (5-0.65)/0.02 = 87Ω to pass 20mA into the base.
If your motor requires more than 0.2A, you cannot do it with a simple NPN, you will need a Darlington, or FET.