Normally, the poop will look long and stringy if it's internal parasites. It could be internal problems, but I'd assume it's constipation until it shows other symptoms. Fast it for a couple days. If it was weak and acting sick, that might not be a good idea. Since you think it acts fine, fasting might be the best thing at first. In 2 days, try feeding the inside of a cooked pea that was frozen..not canned.