Oh, I found it. The doctor cannot heal himself. Dunno if it's a standard of the game or not, but since the first game we played here in VGC I was the doctor and I tried to protect myself and I was told I couldn't (and died because of that), I'm adopting that rule (that means, if I as a doctor couldn't protect myself, then I won't allow the doctor to do it)
And I'm sure I didn't make any mistake, by the way