I bought a new bike about 6 weeks ago, I only recently needed to pump up the tyres.

I pumped up the front because it was low and while I was there I topped up the rear. I rode to work then at the end of the day the front is flat. I bought a new tube and installed it, pumped up both tyres again. Next morning the rear tyre is flat... Again after a pump it would last the day before needing to be pumped up again.

Same issue with both after topping them up. Why? I don't get what caused it. The tubes are Presta Valve Schwalbe Extra Light (406). What could I be doing to them while pumping to cause the slow (maybe 2-4psi per hour) leak?