How long have you had these symptoms?
SIN-to-mi — stress on first syllable. The 'o' is closed. Plural of 'sintomo'.
A doctor will ask you this. Learn to understand it and respond with 'Da... giorni/settimane/mesi' (For... days/weeks/months).
'Da quanto tempo' introduces duration questions. 'Da' + time expression means 'for' (a duration up to now): 'Da tre giorni' = 'For three days'. This is different from English — Italian uses present tense where English uses past continuous: 'Ho la tosse da una settimana' = 'I have had a cough for a week'.
Da tre giorni.
For three days.
Short answer to the doctor's question about duration
Da una settimana circa.
For about a week.
'Circa' means approximately — useful when unsure
È iniziato ieri sera improvvisamente.
It started suddenly last night.
Describes sudden onset — important diagnostic information
'Tachipirina' (paracetamol/acetaminophen) is the most common over-the-counter painkiller and fever reducer in Italy. It is a household name, much like Tylenol in the US. Italians often say 'prendo la tachipirina' rather than 'prendo il paracetamolo'.