URGENT!!! Just noticed a lump on my cats neck. He is an orange tabby, 3 to 4 yrs and 12lbs.?

Petting my cat and just noticed a lump under his jaw to his right side. It feels squishy but it definitely appears to be getting bigger. First noticed yesterday and it was so small and he is so furry I couldn't be sure but it is definite today and you can see it without even feeling now. I thought the worst at first, cancer. But now I am wondering if it can be an infection. Looking for sound advice as soon as possible. Thank you