I'm betting the water is just too cold and the beach has been pounded. Maybe it's sanded in too. Don't sweat it though, as we all go through droughts.
After a few unsuccessful hunts for caches, jewelry, gold nuggets, meteorites, etc I will go hit some parks that have produced for me. -- Sometimes you need some easy "wins" to make sure you and your equipment are doing well. A good test garden will also help to boost your confidence as you can make sure everything is working as it should be.
My guess is everything is fine, just more that you're in a slump. You didn't get that many crusty pennies by accident... Keep swinging and stay optimistic, as the good finds WILL return, it's just a matter of time. And remember; a "bad" day of detecting is still better than a day spent toiling at work!