Can you show us how you have it wired up?
Posting a picture of a pencil and paper drawing is good enough.
Do you know that you need to go parallel? If it works on only on side, you might be good to go.
My guess is that you don't know, because you are likely doing bench testing with the motor unloaded.
Once you put a wheel on the motor and put it on the floor, the motor will be loaded and it will pull more current.
Edit: if all else fails, there are more modern motor drivers like the Pololu DRV 8838 for single motor drivehttps://www.pololu.com/product/2990
or 8835 dual motor driverhttps://www.pololu.com/product/2135/specs
The have 1.2A per motor.