If it is thrush, then I would avoid the glycerine to clean his mouth as glycerine is sugar & thrush thrives on sugar.
It spreads quite quickly so just check the insides of the cheeks, tongue & even inner lip
Regarding solids.........there are a lot of links I can send you why you should hold off until lo is 6months
I don't like telling people what to do(I would rather just give them advice & proof of articles & let them decide for themselves) but I research a lot of things regarding children/parenting etc as I never really did that with my 1st child & also made the mistakes of formula feeding her, starting too early on solids because what doctors say to you etc. so I wanted to learn as much when I expected my 2nd child.
He is 16months now, still bf him, started solids - slowly when he hit 6months but I let him guide me. Never gave him rice cereal as those cereals are all just sugar based and contains no nutrition.
If you'd like, I can email you some links regarding the virgin gut of a baby and links on rice cereal etc and then you can decide if you want to continue giving solids or hold off. I also have a fb page where I post a lot of links about various topics - Researched and Informed Parenting
Just remember, a nurse, clinic sister, doctor, paediatrician etc can't give advice of nutrition as they are not specialists in that field and give more wrong advice than right. I know a lot of people will always say you should start so early because baby is hungry, isn't picking up enough etc etc but remember, if he is more hungrier, than he will bf more often. I don't watch the clock with my son, I demand feed him till this day as bm digests very quickly.
Okay, okay, sorry for the long essay hahahaha