Well 300 grams means less than 6 months old (except in very rare cases)
As has been said 1 week without eating is nothing to a BP. They can and will go off feed for weeks and sometimes months at a time for no apparent reason.
- How are you housing this snake?
- How are you heating the cage?
- What are your current cage temperatures?
- How are you measuring temperatures?
- Does the cage have hides? if so How many and what type?
- What size/type cage do you have?
Overall your new snake needs time to adjust to his/her new home.
Are you sure you know how to sex a snake? If done improperly not only will you not actually know what the gender is, but you can also easily injure the snake in the process.