What is wrong with my cat?

I have 2 cats a two yr old and a one yr old, ive never had problems with my two yr old but my one yr old since i got her ive had plenty of issues. Within a week of getting her she was infested with fleas and i noticed rice like worms on her butt. I called the vet and they gave me 2 pills one for each of my cats. I cleaned out the room used a flea carpet killer i bathed them both and made sure not to see any fleas. About a month ago i noticed worms again on her butt and bought an over the counter product seemed to work till today she has them again and this time its ALOT. Aside from the worms she also developed a rash all over her body so i bathed her every other day for a month and she seemed to be doing better she has it only on her tummy and neck. Ive tried everything i can and i don't know what to do shes my little love and not being able to allow her on my bed is sad can someone help if you of anything please help.