Does anyone know what this lump is on my froglet's chest?

[Gemma]

I first noticed the lump 2 days ago. The underside of his body is still slightly transparent as he's so young, and 2 days ago I could see that the lump was directly where his heart is (or maybe his lungs. I'm not 100% sure which organ it was that I could see). Anyway, today I managed to get a closer look, and the lump is about twice as big as it was 2 days ago. It kind of looks as though it is 2 lumps merged into one now. He's got a healthy appetite and he's not showing any other signs of illness. He's behaving exactly the same as all of the other frogs. Does anyone have any idea what this could be? It doesn't look good :(


Sorry about the dirt in the background. I took these this morning right before I changed their water.