How do you say

I lost fifteen pounds in three months, but my stomach won’t shrink.

..in Chinese?

三个月内我瘦了十五斤,但就是没办法瘦腰。

sān gè yuè nèi wǒ shòu le shí wǔ jīn , dàn jiù shì méi bàn fǎ shòu yāo 。

How do you say "I plan to learn to cook in the next three months" in Chinese?