Eggs with very thin or no shell & no yolk

Hi guys,

I am new to the egg game.  I have 2 backyard chooks & 1 isn't playing the game properly.  She is a Sussex chook.  I have only had them for about a month.  She was laying normally, then the eggs started to get pimples (extra bumps of shell on the outside) on them.  Now she is laying eggs that have a very thin shell, if one at all with no yolk.  I can't tell what size they would be as they are now eating the contents!  Which is another problem!  They are fed commercial layer pallets (they have an auto feeder)  along with mixed grains and household scraps.  No potatoe skins as I hear that it is bad for them.They have a supply of shell grit available to them all the time and an automatic waterer, so fresh water all the time.  They are allowed to fre range in back yard nearly every day, so what am I doing wrong?  Please help!

I am unsure how old she is ...........  I bought her a month ago and she was already laying.  The people I bought her from had purchased her that day from an auction, so they don't know either.  I have spoken to a vet an he said to give her some calcium, so I have added calcium powder to their water.  He seems to think it might be "HER" problem and there may be not a great deal I can do about it.  But I will try anything to see if it improves.