Help me

What year should I start solving past papers for? I feel so anxious and I am having a panic attack. I don't know what to do. I am currently at chapter 16 in CIE biology and I still haven't studied for Physics and math. I dont really have a problem with chemistry since it's easy for me. How and when am I going to solve past papers?! Please help me. I feel like I'm going to faint.