My prediction is that you are hard foot driver. Means drive car at high RPMs.
Because I have observed one thing about my car. I change oil at 4.5~5K (using Delo gold 15w-40 Diesel engine oil in my Petrol Car).
When I travel within this city, then oil reduction does not happen. But when I travel outside city (usually I drive 3.8~4K rpms at speed of 135~145km/h continuously for 2~4 hours), then some oil reduction happens. But this does not means my engine has become weaker. It just have to deal with extra load.
5w-30 is an ideal oil for all year usage. I will suggest to keep using it. But you may try to change the oil company in same viscosity.
Using 20W-50 is not suggested.