How much of the salt you been using? Usually when fish has internal problem Epsom salt is recommended. Epsom also helps to purge parasites out. I think you guy has internal and external problem though. So if you really think he is better after salt dips you can continue it. You can dip him more than 2 times if you think its helping.
Try to feed him throughout the day as much as you can, he need to eat to stay strong.
White poo indication of internal parasites or some kind of internal bacteria. I would still try to find General Cure . May be other store carry it ? Or if your store out of stuck ask when they will get it. See if you can find Tetra Parasites Guard.