Need help with item triggers

I've made a trigger wich would activate a few things after a horn is blowed (An item) but as I click on the item, and after the item ability finishes, nothing happens.

I changed the trigger so it would be activated by a potion of healing and it works. What's wrong with custom items???.

I also made my horn item from a potion of healeng and yet, nothing happens. What should I do???

Does the horn have unlimited charges? Infinitely charged items don't trigger the use of an item.