You need to consult child development specialist or child psychologist. There is definitely delay in language.
Proper assessment is needed in all sphere s of development. Like gross motor, fine motor, social and language.
Regarding immunity,
babies usually catch infection Frequently in play school but do not lose weight.
Please check weight and keep record of weight. If loosing weight , surely ... Than need to investigate.
Next Steps
show to child specialist as soon as possible