Yeah that certainly isn't starving. 3 weeks is a blink. I go 7 plus months plus with our royal.
As stated be patient. A burm WILL take about anything when it is good and ready.
Just wait it out. 2 months is nothing. I have a coastal carpet that gets weird once in a while. She just smoked a large rat after i decided to wait it out.
Unless there is a glaring health or husbandry issue, your snake will eat in due time, and probably will be voracious from that point on.