Cannot Find Exp Share in my Inventory

[Loneconkorror]

Hello PRO team, 

I used to have a Exp Share in my inventory from when I started the game up until some point in the Hoenn region (where my progress is now). I used to have Exp Share in Hoenn but it has suddenly disappeared. I noticed its disappearance around the time of the Valentine's Event, but I had Exp Share before that because I acquired it from the Aide's in different regions (Kanto, Johto, and now Hoenn). What can I do to get it back? I'm trying to level up my Pokemon and without Exp Share it is very tedious  Thanks for your help!