Cold Sore Virus?

Does anyone have any idea what this virus is? My son is 20 months the last 2 weeks he has been so fussy with food and barely eating. On Tuesday at childcare he started getting a temperature and just look out of it. Super grumy and crying all the time. On Wednesday developed two blisters near his mouth thought it was eczma and today heaps of blisters around his mouth and inside his mouth. He can't eat at all and cries constantly because it hurts and he's only drinking milk from a bottle. Not even sipping water so I'm mixing water with his milk before he goes down for a nap/night sleep. I have my wedding in 2 weeks and he's the ring barer. No other blister/pimples on hands and feet so not sure if it's that or cold sore virus. What can I do to help it go away fast? Will there still be marks in 2 weeks?