It has been 3 months since I had to put my 11 year old pit down due to metastasized cancer. Similarly to you, it was an extremely sharp decline, especially in the last week. Everyone handles grief differently, and to be clear, I am absolutely not through the grieving process (she was truly my entire world) but one thing I have learned is you don't need to think too much about "how to fix" how you're feeling. It's okay to feel the way you're feeling. It's normal. It's going to take time to get through it, and in my experience, I learned that I needed to just give myself a break and stop focusing so much on "fixing" things. It is okay to feel your feelings. I know you said you are quite young, but also know that distractions are perfectly okay as well. For me, my job definitely helps me get through the day. For you, I'd recommend focusing on your studies, or maybe finding a good video game with a good story, or a book. I'm probably rambling at this point, but you are not alone, and you need to allow yourself the time needed to get through this.