* Was the snake feeding before you purchased it. If it is only 4 weeks old then chances are it's not long shed and may not have actually taken a meal before you purchased it
* If it is 4 weeks old its shape sometimes won't resemble the adult and the back bone may be more pronounced. Difficult to advise with out seeing a picture
* Assist feeding is not something that you should not be doing so soon. It is far more likely to stress the snake out than to get it feeding.
* You need to provide details on how you are housing the snake - temperatures are low.
* Is that night time drop on the hot side or cold side