If you have an hatchling on your hands then you need to provide proper husbandry.
Force feeding is not something recommended lightly and should only be done when all other options have been exhausted.
Assuming you have an hatchling you need to do the following.
Get a 6 quarts plastic tub (15 quarts at the very most)
Use aspen as bedding
Provide 1 or two PLASTIC flower pot saucer
Provide a hot side of 88 degrees.
Leave your BP alone for a week, NO HANDLING
Offer a live appropriately sized mouse (equal you BP's girth size)
55 gallons will not work with an hatchling even if cluttered a smaller tank will likely not be a better option either.
While adults can go off feed for a long time an hatchling should be VORACIOUS and should be eating.
Also pinkies if pinkie mice are also not appropriated for a BP.