The masses that you are feeling may be enlarged lymph nodes or salivary glands. The reason may be infection, or something more serious, and veterinary exam is needed to see what the swellings are. An allergic reaction is unlikely, since allergic reactions usually cause a swollen face/muzzle or hives. As long as he is eating, drinking and breathing normally, then it can probably wait until Monday, when your regular veterinarian is open. You can also look online for low cost veterinary clinics in your area.
Good luck,
Kimberly Coyner, DVM
Large lymph nodes big enough for pet owners to feel may be due to cancer called lymphosarcoma also. I'd make sure to bring your dog in for a veterinary exam!