This sounds like anxiety to me. Might be helpful to seek out some mental health resources, if accessible.
Beyond that, good feedback is based on assignment criteria/the rubric, specific, and designed to help students improve. Avoid positive and negative statements with no explanations. Pose questions to help students think about things in a different way when offering constructive criticism. If you can, build a bank of comments and resources for common issues so that you can improve your efficiency. Unless you're literally correcting, don't mark every single error. Focus your comments on the big, substantial issues. Offer more feedback on formative assignments. Use language that students will understand; explain disciplinary jargon.
If your colleagues are great, consider asking one to offer feedback on a student artifact you're grading, then discuss any discrepancies. You've got a rubric and good colleagues, which means you have more guidance and resources than many instructors have when they start grading, unfortunately. It will feel more natural over time, but you can also look into professional development in the meantime. Sign up for teaching workshops. Read research on grading and feedback. Check out some seminal how-to texts.