either youre nervous about the content youre trying to communicate cause your skills in italian arent solid enough or the other answers are probably accurate. my native language is german and i have trouble with my voice there
when i speak english on the other hand my voice is deep and resonant, because i have strong impressions of american actors from all the movies i watched. i was recentely in london with my english class and theory seamlessly became practical. actually i felt like my entire personality changed a little everytime i spoke english in real situations, in contrary to just practising with fellow germans. so take the advice by brianjtarr, find italian actors, news anchors, whatever, with great voices, listen to them and get into a fitting mindset when speaking yourself.