<s>[INST] my 18 month old son has asthma but also keeps getting chest infections, at the moment he has a nasty cough which he is coughing up a froth like liquid (smells a little like vomit but doesnt look like it) what could it be? he   cant sleep,hes crying when he coughs, his appetite poor and several dirty nappies a day. he had bronchitis at 3 month old and a chest xray last week wqhicChatDoctore back clear, im confused with the clear chest but the constant cough [/INST] Hi, constant coughing with mild expectorants in kids can be due to acute pharyngitis, acute bronchitis, pertussis, sinusitis, flu etc. If he is also having asthma as stated by u then he should be given oral-syrup antibiotics with other supportive treatment immediately. For that u take him to pediatric doctor and get investigated first by all routine blood tests and don't relay only on chest x-ray despite its normal. </s>