Asthma Exacerbation: Given the history of using salbutamol last year with similar symptoms, and the current presentation of wheezing, cough, and shortness of breath (SOB), asthma exacerbation is the most likely diagnosis. The symptoms of scale, intercostal, and subcostal retractions, along with a fever, also support this diagnosis.

Acute Bronchiolitis: This is a common condition in young children, especially with a history of fever and respiratory symptoms. The presence of wheezing and cough could suggest bronchiolitis, especially if the child is under 5 years old.
Pneumonia: The symptoms of fever, cough, and SOB, along with the physical examination findings, could also suggest pneumonia. The use of salbutamol in the past does not rule out pneumonia, as wheezing can sometimes be a feature of viral or atypical pneumonias.
Viral-induced Wheezing: Some viruses can cause wheezing in children, similar to asthma. The history of similar symptoms in the past and the current presentation could suggest a viral-induced wheezing episode.

Foreign Body Aspiration: Although less likely, foreign body aspiration can cause sudden onset of respiratory symptoms, including wheezing and cough. It's crucial to ask about any history of choking or playing with small objects.
Pneumothorax: Tension pneumothorax can cause severe respiratory distress, and although rare, it's a life-threatening condition that should not be missed. The presence of severe retractions and decreased oxygen saturation could suggest this diagnosis.
Epiglottitis: This is a rare but life-threatening condition that can cause severe respiratory distress, stridor, and difficulty swallowing. Although the child's symptoms do not fully align with epiglottitis, it's essential to consider it in the differential diagnosis.

Cystic Fibrosis: Although rare, cystic fibrosis can cause recurrent respiratory infections and wheezing. The child's age and symptoms could suggest this diagnosis, but it would be less likely without other supporting features such as failure to thrive or recurrent infections.
Congenital Heart Disease: Some congenital heart diseases can cause respiratory symptoms, including wheezing and cough. However, this would be less likely without other supporting features such as heart murmurs or failure to thrive.

To write a SOAP note, consider asking the following questions:

Can you describe your child's symptoms in more detail?
How long has your child been experiencing these symptoms?
Has your child had any fever, and if so, how high?
Has your child been using any medications, including salbutamol, and if so, how often?
Has your child been exposed to anyone with similar symptoms?
Does your child have any history of allergies or previous respiratory problems?
Has your child had any vaccinations, including the flu vaccine?