Hi,
Thanks for asking the query,
Fever along with blisters needs to be evaluated, a basic blood count will help.
For fever you can give paracetomol in correct dosages, please take your baby to the
Pediatrician.
Do not brush the teeth till the blister heals as it may worsen the condition.
Take your child to the Pedodontist and get the thorough clinical evaluation done.
Swollen gums along with pus formation can be due to improper
oral hygiene, scurvy, bacterial and fungal infections. It can be a serious
sepsis.
If your child is taking some antibiotics for fever it can be due to reaction to antibiotics and other drugs leading to ulcers on lips, gums and tongue known as steven
johnson syndrome.
Make sure that your child drinks plenty of drinks and water, milk, fruit juices.
Hope this helps out.
Wishing your child a healthy recovery!
Regards...