At one point hackers did get access to your account, so it is good you changed your password.
The problem though is it is easy to "spoof" and email to look like it came from you, when in fact it did not.
If you look at this site, it shows how easy it is to do this where you can send an email to anyone with any from address.http://www.sendanonymousemail.net/
There you see you can enter any senders address.
The problem is that due to how email is made it is impossible to stop this from happening. It's just the way email works. Similar to sending a letter, as on this you can put any address on the back of it claiming to be from anyone.
The only thing to do is make sure your password ***** ***** So for example if it is ilovepizza make it 1l0vepizz@
Just a few characters in place of words will make it near impossible to crack and unless someone specifically focuses on you, you will be safe. Also, never email your password ***** anyone even if the email site "claims" to be asking you for it. And inform all contacts you were hacked in the past and that any emails that look suspicious and especially with strange links, they should delete immediatly.
Eventually these emails will stop, it just takes some time for the hackers to lose interest in your address.
If you would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service, that would be greatly appreciated.