Lump that grew in one day

[Aga]

Hello. A few days ago I clipped my sow's nails. At that time I also checked her fur and skin etc. The next day I noticed a small bald spot on her back. There was a lump of a cherry diameter. The lump is well-rounded, moveable and is of thick jelly consistency when I touch it. There are no signs of inflammation. She didn't not react at all when I touched it so I assume that it is not painful. Her behaviour is as usual, I didn't notice any change in behaviour or eating patterns. Unfortunately our vet who specialises in guinea pigs is on holiday and we can go for appointment in second week of January. Earlier we can go only to cats & dogs vet. Do you have any idea what this could be? I read about sebaceous cysts and lipomas in guinea pigs but the strange thing is that it grew to such a size in just one day. I attach some pictures.

 

[Piggies&buns]

If it has grown quickly and is so continuing to grow then the lump really ought to be seen much sooner than the second week in January.

A lump needs a hands on check as there are several things they can be.

 

[Aga]

It grew to this size in one day and then stopped and stays the same.