well my advice is to first calm down, the reason you have been going to the toilet so much is because you are extremely nervous. try to have breakfast, take your mind of it for a while, and revise in your head, but don’t make yourself worry too much as you have revised a lot, so you should be fine.
as for the whole new thing. it isn’t that new, it will be a hall (maybe it will be cold so i advice to wear something warmer and no hoods, they are not allowed). There will be a lot people in there, some might be doing a biology exam (or whatever exam they have at the same time as you), so yeah make sure you know which time your exam ends. i personally advice you to go early look around the exam hall, get a bit comfortable. don’t be scared its nothing new, just different. Read all the instructions on the paper, and what the invigilators tell you, you can ask for help, or water if you have problem, they are there to help.
i hope i helped. good luck. you will do great.