I can't heal my Pokemon.

[Diamondowner]

I have already beat the Elite Four and the Champion.
I'm just doing little side quests and stuff and my cousins and my brother have the games too so I play with them.

And while I'm leveling up my Pokemon, sometimes they get hurt so I use potions on them, but when I give it to the Pokemon it says it won't have any effect! On any of my Pokemon! So I need help. :[

[The Real AAA]

Do you mean like Iron, Zinc, etc

[Ichida]

HP Up, Protein, Iron, Calcium, Zinc, and Carbos aren't potions, they're Effort Value vitamins. Potions, Super Potions, and Hyper Potions are used to heal HP, and the "Restore" and "Heal" items are used to heal status effects like PRZ (Paralysis), FRZ (Frozen), BRN (Burned), PSN (Poison,) etc.