Ok, I hope we're not making your homework ;P 1. "Desde que descubrí que no cabía en mi ropa vieja" seems the beginning of a sentence, or at the most, a short answer. It means "since I found out I didn't fit in my old clothes", so you can say it is grammatically incomplete, since the whole sentence is more of a "temporal" verb complement. The sentence could be right, in my opinion, if it was for example "Desde que descubrí que no cabía en mi ropa vieja, empecé a hacer ejercicio". 2. "Sara fue a trabajar a pesar de no sentirse bien" is correct. As you may know, it means "Sara went to work even though she didn't feel ok".

the second one is correctly, since the first needs to be complited.

Gramaticalmente hablando, la segunda.