Nic, both my biggies had hand/foot/mouth (coxsackie virus). One blistered on the feet, one in the mouth. Try the numbing gel sold for teething babies, can't think what it's called. IF he'll let you put it in there! It will go within a week Just very dramatic when it happens!
We have no hot water AGAIN due to the rains last night. Grrr.