Keep your fingers crossed for little Alvin

My little Gerbil, Alvin, has not been himself for the past week. He's off his food, and as Alvin is normally a bit of a glutton, this has me worried.
He is around a year old, and I've attached a picture of him, he is the white gerbil. We really love him, as well as his 5 brothers (Simon, also in the picture, as well as Theodore, Damien, Basil and Manuel- they live in groups of 2).
Please keep your fingers crossed that he will get his appetite back!