Both kidney and liver problems usually have increased water intake and urination.
If possible, have one of the docs listen to the cats heart and lungs. Murmurs in cats often indicate heart disease. The normal rate is around 170 beats per minute. This is hard to count until you get used to it and learn to count fast. Over 200 may indicate heart disease.
I've had some luck treating non specific illness empirically with antibiotics. Pediatric amoxicillin (50 mg twice a day) or augmentin (62.5 mg twice a day are good choices if available.
I've used prednisone empirically also....back in the days before easy access to blood work, ultrasounds and other instruments of modern technology. In addition to being a good antiinflammatory, it also stimulates appetite. I'd use antibiotics first and 5 mg of pred a day for no more than 5 doses if the antibiotics don't work.
Another thought is parasites. Roundworm and tapeworm are the most common in the US. I do not know what others might be common in Yemen. Let me know if you or your docs know. Pyrantel is a good treatment for roundworm and praziquantel for tapeworm.
There are some veterinarians, particularly working in agriculture, in Yemen. Are you able to find any to ask about common cat diseases and parasites that may not be on my radar as an American vet?