Sorry, I hadn't had a chance to post. The lump had indeed grown. When the vet stuck a needle in to aspirate it, he realized that it was a small hematoma. He drained it and took a look in the microscope. He said that he was pretty confident that it was all blood and that there was nothing to worry about, but he will send it out for analysis just to be safe. He's not worried, though, so neither am i .
ETA: the bill was $51!! who ever heard of a $50 vet bill!!!! i love this new vet clinic!