Red and swollen under tail.

[brierose3]

My hen has a red and swollen lump around her bottom that I just noticed today. We got her a few days back and she seems really skinny but has been laying eggs. We are new to chickens so don't really know what it could be. Any ideas?? Thanks

 

[brierose3]

Also just then I checked her over and when I moved some of her feathers on her chest I noticed a similar lump though smaller.

 

[ABourdon]

Did you ever work out what this was? My barnevelder has exactly this too!