De-worming isn't immediately effective and if there are parasites generally requires at least two courses (excepting the ones which must be treated by antibiotics). The first may kill the existing 'adult's' but those adult's have likely produced larvae which the second course is designed to catch after the appropriate time (this is general and there are slight variation's per parasite) Also, was the parasite diagnosed and treated by your veterinarian? If not, you may not have used the correct de-wormer. Different parasites require different treatment's. The OTC ones found in grocery and pet stores primarily only kill one type of parasite and have a very high incidence of severe illness and death even when used on label. There is also the possibility there's something else going on.