If the vet tells you that they do not have a parasite and do not need medication you can try some slippery elm bark (the same kind that humans take). I use 3/4 cup water and empty 3 capsules into the water and boil until it becomes slimey and then give one tsp. mix in the food.
This has helped my 3 cats whenever they have episodes of diarrhea. Hope this is helpful.
MartyG
You might want to take them to the vet. I know it can get expensive but I just found out all 3 of my cats have Giardia. They all caught it from one cat and I think she may have caught it at the vet where I took her to get fixed. Giardia is an intestinal parasite and is very contagious to all animals and people.
I hope you aren't changing the cat box. Since you're pregnant, you really should be having someone else do it. And have everyone wash their hands with hot,soapy water for at least 30 seconds everytime they change the cat boxes and even after petting them.
If it is worms or parasites, you really need to have them seen and treated or they'll just get worse. If left too long, it can even be life-threatening. I'm not saying they have that, hopefully not, but if they do, you really do need have them seen. I hope they feel better soon!