Hi Nishan.dj,
When the engine is cold, remove the radiator cap, make sure the coolant is there to the top of the radiator and to the appropriate level of reserve tank and start the engine. Inspect the radiator for water bubbles at the radiator cap hole. If air bubbles keep coming out (when engine is getting wormed, the frequency of the bubbles will also rise) it could be a head gasket leak.
However, there is a small problem when performing this test. That is, when the engine is getting wormed, water (coolant) get pressurized and will overflow from the radiator cap hole and it will be a mess. So, in order to fix it, get an empty plastic (preferably white) mega bottle, fill water in it about 25% of the bottle and place it upright on the radiator cap hole. Now you can hold the bottle and inspect for air bubbles for a considerable time.
If it is the case (double check with your mechanic), and if you are going to change the head gasket, once the cam is removed, inspect the cam head for for cracks (near adjacent cylinders). Make sure to plate the cam head before installing the new head gasket.