What Causes Feeling Of Lump Inside Throat While Having Antibiotics For Throat Infection?

its for my sister, they told her she has a throat infection and they prescribed her antibiotics and the doctor also noticed she swollen on her left side of her neck, she said it might be goiter, she not sure. My sister is going for an ultrasound on monday, but the only problem is she feels a ball in her throat and it has white pus on it, she just afraid it might swell up even more.