I believe this is a Sardinian warbler nest, location and timing are bang-on too.
At the moment the Sardinian Warblers are really busy (and noisy!) the males are super charged and you’ll no doubt see them in song flights.
Nest building is now and some even laying (most in March) with clutches of 3 – 5 eggs. They have 1 – 3 broods per season and the nest is usually 30 – 60cm off the ground although exceptionally 3m!