The Pigeon Antipyretic Plaster with eucalyptus oil is actually recommended from 6 months, so at 4 months it's better to use the regular Fever Cool Plaster instead, that one is safe from 0 months and lasts up to 8 hours. For the blocked nose and phlegm, my neighbour brought her baby to the PD and was advised to use saline drops and a nasal aspirator rather than any chest plasters at this age. Do check with your own PD though, since every baby is different at this stage.