The first thing a doctor wants to know is how long it's been going on: Da quanto tempo sta male? — How long have you been unwell?

Italian answers with da + the time — and the verb stays in the present, because it's still going on:

Italian	English
Ho la tosse da tre giorni.	I've had a cough for three days.
Sto male da ieri.	I've been unwell since yesterday.
Ho mal di testa da stamattina.	I've had a headache since this morning.

One little word, da, does the work of both for and since. And English I have had becomes Italian ho — don't reach for a past tense here.