Hi first_c,
Actually you're looking for two different but related bits of info.
If you want to know when someone's replied to your posting(s), the simplest way is to "subscribe" by ticking the Notify-of-replies box when you post. You'll get an email notice each time there's a reply.
To see where you (or for that matter, anyone) have posted recently, click on the symbol for your profile (or the other person's). When that comes up, down at the bottom there's a link to show your most recent posts. The default is the last 10, but you can select the last 5, 10, 50, or even "all".
Best,
Mike