I rarely bite at these posts.
For starters, skinny does not equal sexy. It so saddens me when I hear women say that because I think that type of mentation is what fuels body dysmorphia and eating disorders and a host of confidence issues. There are all types of sexy and it's 99% in the head. In my opinion, confidence equals sexy.
But in these parts, strong largely equals sexy. And it's one of the things I absolutely love about the sport of competitive powerlifting. Strength is hard work. Strength is accomplishment. Strength is sexy. Skinny for the sake of being skinny has no place in this sport.
Do you realize that 5'7 at 140 lb. and 18.4% body fat (not sure how it's measured or what the relevance is) is not remotely "fat" for a woman? Wherever did you get the idea that it was?
That being said, I understand the point of female powerlifters playing with weight classes to find where they're strongest. But I think you're too early into the sport to worry about that at this point. And your efforts at doing such have caused your lifts to stall. So what's important to you? Getting stronger in powerlifting or being skinny (which has no real intrinsic value in this sport)?
If you love the sport and are truly serious about trying to make it to IPF competition levels, I'd say stop worrying about the scale for now. Focus on hard work and eating clean. If you do that, the scale should naturally settle, which I would think would be in a pretty aesthetically pleasing place.
Good luck to you!