Search
In the dark green bar at the top of the forum, on the right, click on Search. This takes you to the Search screen.

This screen offers many options to narrow your search. Searching in a single subforum usually works better than searching the entire forum. Choosing to show results as posts rather than the default of threads can make it easier to find what you are looking for if it's buried inside a long thread.

Including a username in the search can help you find posts made by a specific person.

You can use Search to find posts from a specific time period, so if you want to see posts made in the last few days just set that time period in your search without specifying anything else.
Alternatively, you can use a link like this: http://amblesideonline.org/forum/search.php?action=getdaily&days=2 (but change the number after "days=" to be the number of days you want) to see posts from the past few days.