I was playing and I fought a bit with my terriermon and got a card every time but I reset and have been playing with my Lopmon and every fight I win I don't earn anything. Am I doing something wrong? Or is it not guaranteed to give you anything on a win? I really need new moves lol 

There is a limited number of attacks in the game, and each stage drops attacks that correspond to that stage, You can only have one copy of the attack card saved at the time so the enemy won't drop a new attack card if you already got it.