My male Guinea has had what looks like a growth instead of the normal helmet. It never seemed to bother him but recently started getting larger. He still hasn't acted sick at all but today it looks like it has ruptured and has bled some - he is shaking his head now and then like it is hurting or uncomfortable - any idea what to do with it until I can call the vet tomorrow? The other two guineas are fine. He is about 18 months old.