Lump lump under arm?

Sorry. I have never seen one. I hope others will be able to help.

It could be an abscess, tumor, cyst or lipoma. There isn't anyone here who is going to be able to tell you exactly what the lump is or how to treat it without knowing what type of lump it is. You need to take your pig to the vet.

It couldn't be a tumor because it hasn't grown...she's had it for maybe close to a month and she eats fine and everything. Can they die from a abcess?

Since you are not a vet, you can't rule out a tumor. Some tumors grow and some don't as fast. They can die from an abscess if it's not treated. The abscess can burst and send infection through the entire body.

If she's had it for a month, why haven't you had it treated already or asked about it before now?

If it's in her armpit, it most likely involves a lymph node. It could be a lymphoma tumor (rare--most lymphoma tumors are in the dewlap), an abscess, or a swollen lymph node due to infection or cancer elsewhere in the body. I would definitely take her in.

Just so you know, not to terrify you or anything, my pig Doom had lymphoma and his tumors would pop up at a certain size and stay that size, not growing, but he kept getting more and more tumors.