Even though I thought I had lost weight, I hadn’t.
〜〜のに
Even though 〜〜, although 〜〜
思ったのに - even though I thought, even thought I felt
痩せたと思ったのに- even though I thought I had lost weight, even thought I felt I had lost weight
Feelは体がスッキリ気がした思うより感じるだからfeelの方が良い。
痩せる - to lose weight, to get thinner
痩せてなかった - i haven’t lost weight, stayed the same
前はlost weightを言ったから痩せてなかったの時 “i have(lost weight)” とか “I haven’t(lost weight)” だけで平気です。