Is it possible to find out what its diet was at the time of adoption? If so, then give it that diet to start with.
During the mating season, dogs have little desire for food. Again during the hot summer months they prefer to eat at night or early morning.
They also need long walks especially early in the morning not only as exercise but improvement in appetite. Pay attention to its grooming too. Watch out for ticks and fleas.
Does it have foul smell emanating from its mouth? If so, then the foul smell could be more than just a dental problem.
Check for worms. Has it been dewormed?
Check its stool. Is it too hard or too liquid like?
Has it been dewormed? Keep an eye on its stool texture.
You have mentioned doing a blood test. Were the kidneys, lipid, and liver profiles normal?
It is five years of age. If u have given it a round of vaccinations covering distemper, parvo, influenza and rabies then avoid further vaccinations. Senior dogs should not be vaccinated. It is better to introduce homeopathic nosodes that are given orally or intranasally.
I would advise to kick off the habit of giving it commercial packed food like Pedigree which is of the worst kind. These packed commercial dog food use ingredients that are not fit for consumption but masked as kibbles, and use preservatives which can be very harmful to canines. As preservatives they use ascorbic acid, vitamin C which is produced naturally in canines and excess of the same would lead to kidney problems.
Give it home food of rice and curd in the morning and rice and meat in the evening. Better still give it brown rice like the Patna variety rich in B complex and most all minerals. The white variety has nothing but starch. The food should give an appetizing smell. Do not give it cooked or boiled bone but rather raw three to four times a week to clean its teeth and exercise its jaws. Chapatis are hard to digest unless broken into small pieces and then fed. Do not give it milk or cream. If u are a vegetarian then u may replace meat with two boiled eggs and saltless dal and in place of bone u may give a medium size carrot or apple. Add some garlic. Give it small amounts of paneer only once a day. Do not give it sweetmeats too often.