Swampy I did what you suggested and it still happens.
The simple answer is that in the upper right hand corner of the forum page will be a "stop watching" button. Press it to stop getting email (but see below for a complication)
It doesn't have anything to do with whether or not you are a forum member -- you can watch a forum that you aren't a member of, and be a member of a forum that you aren't watching.
Now for a complication. You might not be watching a forum, but you might be watching threads in that forum. To stop watching a discussion, click on it and press the "stop watching", or you can stop watching using the watchlist application in your profile.
Medhelp tries, by default, to put any thread that you start into your watchlist, so its easy to get threads in there when you don't want them.
Finally, if you don't want any email on anything at all, you can change that setting from profile -> account settings. Uncheck reminder email to not get it anymore.
First off, I am sorry you haven't had resolution to this.
This is a problem some users are having with watch lists. We are aware of it, and are working on it. In the meantime, you can alter your email notifications to not receive emails regarding watch lists. That should help.
To do this, go to your profile (click MyMedHelp at the top right of the page), then click Account Settings just a little bit under that, then adjust your notifications as you wish.
Let me know if this doesn't help, and if you have further problems, feel free to PM me.
Emily