Question

para completar a frase sick yesterday, but i very well today.
uso am, is are was were?

Answer 1

A frase ficaria correta da seguinte forma:

I was sick yesterday, but I am very well today.

Answer 2

I was sick yesterday, but I am very well today.

(Was e were) voce usa pra falar de algo que aconteceu no passado 
was voce usa para : I, he, she ,it
were voce usa para: you, they, we

E (am, is e are) sao o presente do verbo to be (ser ou estar)
Am é usado para: I
is é usado para: he, she, it
are é usado pra: you, they, we