Breastmilk should not be warmed.it should be preserved in fridge on the top shelf and back of refrigerator.you may keep it in room for some time so that it attains room temperature.
Production of milk depends on sucking by baby..it is more in night as
prolactin production is more in night so try to feed baby in night..
You may give expressed milk to baby when you are not available..
It is only perception that milk is less..indicator of adequate milk output:
Baby passes urine more than 6 times in 24hrs
Adequate weight gain 20 to 30 gm per day
There is no other method other than these two to judge adequacy of milk production