Unfortunately on my last visit to Petco someone told me that she should only be fed weekly or every few days.
Um, WRONG. Petco employees usually have no idea what they are talking about. Bettas should be fed every day, with maybe 1 day a week of fasting. I'm afraid to ask but what did they give you for medication? Usually they only have bettafix which can do more harm to the betta then good. It as a tree oil that can damage their breathing organ. If she had fungus, she would have white fuzzies growing on her skin.
I would skip feeding her the pea, I think that is more for goldfish. I
Betta poop should look like little brown cinnamon buns. White poop is usually a sign of internal parasites.
Answer as many of these as you can, in the meantime, I'm gonna go get some others to look and see what they think you should do.
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?
What type of food do you feed your betta fish?
How often do you feed your betta fish?
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?
Have you tested your water? If so, what are the following parameters?
Symptoms and Treatment
How has your betta fish's appearance changed?
How has your betta fish's behavior changed?
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)?