I find two things helpful if I'm am having a hard time seeing eggs.
First, as the others have mentioned have the sun shine over your
shoulder into the cells,  if you are using new yellow comb place one
hand behind the frame so that the light does not pass through the comb.
And second take off your veil.  Some times I see nothing at all in the
cells until I take off my veil and then like magic I can see the little
comma shaped eggs down in the cells.  Good luck
  Rett Thorpe