Hi Eri! I apologize for the late reply ;w; I hope I'm still in time to help!
The antidote is (unfortunately) in Bèla's hands and you will meet him in the room right after the tunnels, where you got stung. If he doesn't appear it's a bug so please tell me more ;w;
This will however lock you from the good endings so if you want to get them you'll have to load a safe file back to the gem chasing quest
I hope it helps let me know if you need anything else! And thank you for playing EmWa >\\\<