Isn't that leg thing a thing only concerning European mermaids or overall just a specific areas mermaids? Not 100% sure but it would make sense considering diff myths in diff countries. What's up with you being a mermaid anyway? Is it some tumblr kin thing or..?
Anyway, I'm pretty sure that in order to lose a big amount of weight in a week you'd have to go on one of those crazy and stupid diets that consist of you starving yourself, so give that weight losing some more time esp considering that you don't seem to do anything too heavy.
Also p sure even thin people don't have a flat tummy without proper exercise, you gotta work on the tummy muscles.
And how tiny are you anyway? 98 lbs is about 44kg???? That's so little.