Have Cat Questions? Ask a Cat Vet Online.
You need to take a stool sample to your vet so that they can give you the appropriate medications. Not all wormers work for all types of worms (and there are many) so you may not be doing any good with the treatment that you are using.
Just scoop up some fecal matter from the litter box and take it to your vet in a baggie. They can tell you really quickly what would be effective and can give appropriate meds for the pregnant cat as well.
Let me know if you still have questions.