1.5 weeks is like a human being about thirty seconds late for dinner. Some people routinely feed hatchling Carpets every two weeks (I think that's far too little, but the fact that some people do it routinely gives you an idea of how bad it is as a one off). Most people feed hatchlings weekly and if for any reason such as a slough they miss a week, they just go until the following week, and sometimes if they're just starting a slough cycle on feeding day and they haven't quite sloughed on the following one, they'll go three weeks. When we're getting babies established it's quite common for us to leave it longer than that just to get them more hungry. I often don't even offer snakes feed for the first time until they're about a month old.
Don't try to feed every second day, especially if you're not trying anything new; you're just establishing a pattern of the snake seeing mice and not eating them.
Unless something happens such as the snake sloughing or you getting a new type of feed to offer or something, don't offer any more than once per week.
No idea what your setup looks like, no idea what your temperatures are, light levels, etc, so I'm not sure how anyone can tell you whether or not you're doing everything right.
How long between feeds is okay depends on many variables such as the condition of the snake and why it's not eating. If the reason it's not eating is that the temperatures are wrong or something is bothering the snake, then that's an immediate reason. If it's just that you're too busy to feed the snake and it was previously well-fed and in good condition, probably a couple of months for a younger one or a year or two for an older one (though in practice I'd be worried if you were too busy to feed your snake for a year).
The three most common causes in these cases are the snake not having been properly established by the seller, the environment being inappropriate (temperature, setup, too much handling/disturbance, etc) or an incorrect method of offering feed is being used. There's no way for me to identify which of these is the case here. It could also just be that the snake is coming up for a slough, though after 1.5 weeks that's unlikely.
