Eggs

I have had hens for just over 3 weeks, they have been friendly charming little girls who have changed from skinny little girls to proper 'hen' shapes before my eyes...and they have started laying eggs!! The two Warrens have small very hard shelled eggs, but today the Light Sussex has layed a soft shell egg that broke as I picked it up, also she did not lay it in the nest box, but dropped it from the perch I think. I am a beginner in all this, so I have had a look on the various forums for chickens , it seems that she may not be getting enough calcium, or she may need worming ( already? she is only just 20 weeks old :-( ) or she may have had a shock....... Well last night we had the most enormous thunderstorm, lots of crashing and lightning, so I hope it was that, such a shame for her first egg experience, but I will keep an eye on her tomorrow and hope that all goes well. I will put some photos up here soon, and I hope to be doing some sketches of them too if I can, but when I sit in the garden they have taken to sitting on my lap so I may have a bit of trouble getting some drawing done......I love how friendly and comical they are ;-)