Pisces is so compassionate that you find it hard to believe when other people don't quite rise to your level. People could take advantage of your trusting, open-hearted nature.
If someone is always taking credit for your work, blaming you for things you didn't do, or taking you for granted, you have two choices.
One is to avoid the issue. It won't change the situation, and you'll have to be content with the way things are. The other is to teach the person how you want to be treated. This takes backbone, but you're up to it!
Don't just go with the flow, speak up. The person will change their behavior - or not. You can then decide whether to continue the relationship.