It may be the pullets laying the shell less eggs, as shell less eggs are more common in pullets and young layers.
There are a few dewormers available that you can use for your chickens. Some of the best ones as Fenbendazole (safe guard), Ivermectin, Eprinex and Valbazen. All, except the Eprinex has a withdrawal period of 14 days. Do the deworming in 2 stages, give the chickens a dose, wait 10 days and give them another follow up dose to make sure you kill any worms that may have hatched since the first treatment. It's up to you if you want to eat the eggs laid during the withdrawal period, but if you are allergic to any medicines I'd suggest you check with your doctor first. I know Valbazen is used in some African countries to treat worms in humans. Just don't incubate the eggs laid during the withdrawal period. It could have a disastrous effect on the developing chicks.
I used Valbazen as it's my understanding that it treats a broad spectrum of worms, including tapes. Placed it on a small piece of bread and the girls gobbled it down. I treated again in 10 days and withheld eggs for 14 days after the final dose. Have just begun eating their eggs again and - boy - I had sure missed them! Those store bought eggs are NASTY!
