No poop

My male foster vomited and had very loose stools a week ago last Saturday.  I saw something I couldnt identify (not a worm  of any type) in the vomit.  He seemed okay for a few days and then a week ago last Wednesday he started vomiting again.   Worried that he had eaten "something" and was obstructed, I rushed him to the vet.  $330 later I was sent home with a bag of RX dry food and istructed to keep him on a bland diet for a week.   I feed him and his foster sister (as they share space) just the RX dry food and microwaved chicken breast as instructed.    One of my cats began to vomit with loose stools.   I started her on the same diet.  No vomit or loose stools.   But I seldom find any poop in the litter boxes.   And when I do, there is very little.   I  feed each cat a piece of chicken about 1" by  2"   shredded 3  times a day and a half cup of the RX dry.    Should I be concerned?   I will be transitioning back to their regular food starting tomorrow.    

Sometimes these things happen for unknown reasons. Usually the culprit is food, but if you've ruled out food then it could just be a "bug" that's going through your cats. I have a large multi-cat household and occasionally these things will move through some of my cats. In fact right now one of mine has diarrhea (and vomiting 2 days ago) and everyone else is fine. When this happens I use slippery elm syrup, probioitcs, freeze dried chicken treats and baby food with no onions or garlic. It's okay to keep feeding boiled chicken for a few more days until their tummies settle. I'm not sure what you were feeding before but you may want to throw out the batch of food just in case it's food related. 

Don't know if this is any help.  Kitty was not pooping and vomit.

Took him to the vet to be examined and Xray.  No obstruction 

from hairballs.  Was giving RXwetfood which he didn't like.

Vet suggested baby food (gerber chicken).  Also, because 

he's on a dry food only diet, he was constipated (maybe)

So what I do now, continue to give him the dry food and

every other day gets a treat of a tablespoon of baby food.

Reasoning for the dry food instead of wet.  The wet food

sticks to the kitties teeth causing tartar which causes other

problems.  Dry food helps prevent tartar as they eat it.

All is back to normal, eating well, drinking water, pooping,

peeing.

try some canned pure pumpkin worth a shot if constipated.
is their vomit "food" or just mucus?
i had a cat allergic to the red dye vomited the red food.
are they eating very fast? he also puked when wolfing down to keep up with the kitties.
make sure you keep them hydrated- add some water to the wet food. you don't want them dehydrated from puking.
EDIT glad it worked out baby food probably keeps regular