I think my iCloud has been hacked
I just got my first iPhone. I use iCloud. Today my mother said she started receiving emails with my name from a Yahoo email addess. I don't have a Yahoo account. Also, the only way they'd know that I send emails to my mother is through iCloud. Has this happened to anyone else. I've immediately changed my Apple User ID password. Does anyone else have advice on steps I should take, reporting to Apple, etc.
Thanks.
iPhone 5