How would I tell if an injection site is abcessing?

[Ezekiel's Garde]

My poor Dew-goat, who has had ongoing mastitis, is now on LA-200, per the vet's recommendation. He doesn't want to test the milk yet, unless the LA-200 doesn't work. I gave it to her subQ yesterday morning (4cc, as she's only 102 lb per the weight tape). Last night, it seemed okay, but this morning, she has a swollen area in her armpit. It's not hard and not terribly warm. I just don't want something going too long, if it is abcessing.

TIA!!!

[RiverPines]

Did you rub the site vigorously at least 1 minute after you gave the shot?
I always rub it at least that long and no matter what shot its is, regular vaccines, drugs, or location, I never have gotten a lump!! In dozen of animals both sheep and goats, never a lump ever!