Ambrolite-S is secretolytic agent so given for thick mucus
Chericof is a cough
It can be given together. but you have said that your child has fever
for nearly 5 to 6 days along with running nose and cough.
It seems he may need a course of antibiotics calculated for his weight now.
Get your child to a pediatrician
he may order some blood test
or start antibiotics.