I love my birds too and lost my Puck, a green-cheek conure, two months ago. We now added Demri, another green-cheek, to the bunch but I still miss my little Pucky-Poo. No idea why he died and thankfully the others (an african grey and a green-winged macaw) remain fine. I am so sorry for your loss...
Please post when you find out what happened to your little one.