Hacking into account

Since hotmail changed to outlook I've had someone hack into my email account numerous times.

I notice as people notify me they received a link from my email that I didn't send or I get bounce back notifications.

I use this email quite regularly for work matters and am embarrassed this is occurring so often.

Aside from changing my password (which I've been making quite complex), is there anything else I can do?

Does anyone have a support number I can call/email.

Question about Outlook Express