What fly/flies were you using? Some flies are more universal than others when you aren't sure what's hatching. My 3 main dry flies are Adams, Light Cahill,
and Blue Wing Olives. One of the 3 will usually work when there are small insects hatching. I also use little foam or deer hair beetles, and they work great for warmwater fish. A #6 Madame X always gets nailed by something.
Pulling a dry fly under can work miracles, even of the fish appear
to be taking flies off the surface. Let the fly land, and give it a light tug so that it's just below the surface 1-3 inches. You'll usually see the take even when the fly is under, so don't worry about that.
If you're fishing 4X tippet, and still not getting any takes, go down to 5X. I was never one to use fine tippet before, eventhough I've carried 7X for the past few years. I usually start at 5X now, and go finer if needed. Go smaller on the fly size as well.
This might seem like a big fly, but it's a #18 Blue Wing Olive on 6X tippet:
There was a BWO hatch, and the real insects were much smaller than a #18.