There's a test to see if your yeast is active enough to use, very simple to do:
Place (open) packet of yeast in a measuring cup and add 1/2 teaspoon of
sugar and 1/2 cup of warm water in the cup and stir all together. Leave in
a warm, draft-free environment for 10 minutes. If, at the end of the 10
minutes, your mixture has foamed up to the one-cup level on the cup, and it
has a nice, domed top, the yeast is active enough to use. Then incorporate
it into your recipe, being sure to subtract that 1/2 cup of water from the
recipe. If you don't get that nice reaction, you should discard the
mixture and start over with fresher yeast.
Susannah