M.R.
My 5, 3 & 1 1/2 yr old all just went thru this.. There's not much you can do :( my 5 & 3 yr old tolerated it well & my 1.5 yr old well same as yours. He sucks his fingers would wake up @ nite.. the only thing was tylenol to ease the pain. I did flavored popcicles to cool his throat.. but you have to force liquids down!!!! I dont care that it may sting!! it's better then seeing them hooked to an IV b/c the #1 thing is they will get dehydrated w/ this virus if you dont force them to drink!!! So every 15 minutes I would force a syringe of water, propel, anything down my kids throat b/c the fever was insane!! But the good news was it only lasted for a few days so they go back to normal. I wouldnt worry about the weight loss they'll catch back up. If you're really concerned call maybe your peds doctor for more suggestions. Good Luck :)