Blow-by is a scenario where the contents of the cylinder during compression and combustion (expansion) stroke escape into the crank case. In case of combustion it's generally hot gasses and fuel that enters the crank case. The fuel contaminates the oil and the hot gasses generate pressure. At normal operating conditions when the engine lube is splashing around the crank case, the pressure buildup causes the mist of oil to escape the crank case through the Positive Pressure Relive Valve into the combustion chamber where it's burnt off.
Reverse Blow-by is a scenario where the contents of the crank case are forced into the combustion chamber.
In both cases the main culprit is the Piston rings, excessively worn piston rings allow a lot of oil into the combustion chamber. In a normal engine a little blow-by and reverse Blow-by is fine, but judging by your condition, I would advise you to have your cylinder measured for any eccentricity and piston rings inspected.
Wrong grade of engine oil is also a factor.
A quick look into the oil level window located at the bottom of the engine does save a lot of hassle. Some bikes are even equipped with dipsticks.
I generally observe my oil level everyday, it give a clear understanding whether the engine is burning or leaking oil.