Robert, Prolific hardly ever send out e-mail invites to surveys. The only way to find them is to log in to the Available Studies page and keep refreshing it. You can automate the process depending on your browser by downloading an add on that checks the page regularly for changes and gives an audible ping to alert you.
I was using Distill with Firefox but since the latest Firefox update Distill isn't fully working and the audio warning doesn't work so I've switched to Chrome browser with Distill addon which is still working with the current version. The surveys go incredibly quickly, I've seen some that want 100 people or more vanish in 30 seconds so you need to jump to the PC at the first bell.I just leave it logged in when I'm home doing other things and try and catch them if it pings. Hope this helps
Good Luck