Breakdown of Desde segunda-feira estou doente.
estar
to be (temporary / location)
doente
sick
a segunda-feira
the Monday
desde
since
Questions & Answers about Desde segunda-feira estou doente.
Why does it use estou (I am) when the English translation says "I have been"?
In Portuguese, when a situation starts in the past and is still happening right now, you just use the present tense. Because you are still ill, you say estou doente (literally "I am ill") along with desde (since) to show when it started. English uses "I have been", but Portuguese keeps it simpler with the present tense.
Could I use sou instead of estou here?
Why is segunda-feira written with a lowercase letter?
Unlike in English, days of the week and months of the year are not capitalized in Portuguese unless they appear at the very beginning of a sentence.
Does desde always mean "since"?
It often means "since" a point in time, as it does here. However, desde can also mean "from" a physical starting location, such as travelling from one city to another.