GiovaneM:
I don't have the datasheet of my stepper, but its a bipolar one and im using driver A4988.
Just because it is bipolar does not mean that an A4988 is suitable. The A4988 is really only suitable for motors that require less than about 1.3 to 1.5 amps. Some motors are designed for higher currents and if you use an A4988 and set the current at (say) 1.4 amps you may be "wasting" a lot of the capability of the motor.
On the other side, if the motor is only designed for (say) 0.35 amps and you set the A4988 for 1.4 amps then the motor will almost certainly be destroyed.
Use your multimeter to measure the resistance of the motor coils.
Does the motor work with my Simple Stepper Code? if not, get that working before trying anything else.
...R