Emails are being sent through my email and it isn't me sending them?

I received all these emails with links that were sent from my yahoo email to my cogeco and when i went in to my yahoo email i noticed all these emails sent that I DID NOT SEND. It happened before and there was a sales pitch in it stating I was requesting my contact to invest??? I don't know what is going on but something crazy is....Gisele Lacoursiere