Ugh!!!! What's wrong with my brain :(

I recently graduated in August and have finally been able to register for the nclex-pn in November. I started preparing for the exam in July and started off doing well on the practice exams I was taking. I'm finding now however that my accuracy rating on practice exams have gone from consistent 65%s and up to being all over the place. Example: one set of questions I might get a 75% or 80% and then another set of questions I'll get in the 40s, 50s and sometimes 60s. It's beginning to nerve me out, in a way I feel like I've forgotten almost everything I've learned in school and I'm not retaining much of what I'm reading in the Saunders review book, Im feeling hopeless like I'm out of time and that there's no way for me to relearn everything before the 21st.

I'm so scared that after 2 long and hard years that all the work is going to be for nothing and I know I have to try as stay positive but I really am having trouble retaining things...I don't know what's wrong with my brain, can't concentrate so I try to take breaks and even days off to clear it but nothing seems to work