It sounds like a case of internal parasites to me. Metronidazole, praziquantel, levamisole hydrochloride or flubendazole are your choices for treatment. Remember though white stringy poo will not mean your fish has internal parasites as it is possible it is only mucous membrane from its intestines.
For Malawi bloat, protrusion of scales, abnormally distended abdomen and popeye are surefire signs. Not all signs though will appear altogether. Causes are often not known as the case happens internally. Rectifying this problem is very difficult. It could have been caused by virus, bacteria or internal parasites, excessive protein intake, or simply the internal organs were damaged from sudden changes in environment.
Please post your water parameters, tank size, tankmates and dietary menu.