It sounds like you are afraid to try and poke out, so you're just hunkering down. But good defense isn't just blocking, it's knowing the right time to get out.
You have to learn the gaps in blockstrings. There are a few ways to do this:
1) Trial and error via match experience. Just play as much as you can, and see what you can do. Ideally, you will want to do this anyway.
2) Training mode. Record common blockstrings that you want to deal with, and figure out where you can disrupt it.
3) Frame data. This should go hand in hand with the other two to show you when you can try for a punish.
A lot of this can also come down to matchup knowledge, so go to the matchup forums for your character, and the other players there will know what moves you can punish against a certain character.
Don't be afraid to get hit. Eventually you'll get the hang of it. Besides, if you just sit there and do nothing all day, they're going to hit you at some point anyway. So you might as well make them work for it.