First of all, keep in mind that everyone has their stronger subjects and the ones they find more difficult. PEDS may just be your difficult subject. That means nothing other than you don't grasp it the same as you may have others in the past.
What have you found to be effective on past tests? How did you plan for them and what was your study style? Follow through with what works. Don't worry about not doing as well as others or as well in on topics as you may be used to. It's normal!
This is your education and will be your career. What you learn from the classes and in clinical is yours to keep. If you don't understand something or encounter something new in clinical look up more information on it. If you don't have time in clinical but KNOW you want to understand something better (be it a procedure or a certain medical problem) jot it down and google it when you get home.
Understand what you learn is the most important piece of the puzzle. You will need to have a solid understanding of everything in order to properly care for your patients as well as to pass the NCLEX so start now.
Since you are in OB and PEDS you are obviously not in your first semester of nursing school
. Take a deep breath.... eat fish.... Take a 30 minute power nap (because I KNOW your not getting enough sleep!) and reflect on what has worked for you, then do it. You might need to just go back to the basics for a minute and get a new start forward.
You can do this. You've done it before. I know you have!
Good luck and keep your head up. You aren't expected to know everything already. That's the reason you are in nursing school. And when you graduate you STILL aren't expected to know everything. Just enough to be safe and the foundation you built to learn more.