Pet Questions? Ask a Vet and Get Answers ASAP
You could be describing tapeworms, hookworms, roundworms.... it's really tough to say.
Your best bet is going to be to take a stool sample by your vet's office and have it analyzed. Most will do this without an appointment and then you can get an appropriate dewormer that will work for the type of worms that your pet has.
Let me know if you still have questions.