let me vent rq

I am currently in my first year of a Medical Science degree, and I hate it.
It's almost laughable, really - perhaps the worst periods of my life oh so conveniently overlapped with me sitting my GCSE's, and again with my A-Levels. My school were never very supportive, despite knowing the circumstances of my home life, personal situation, etc., and so I never received any special consideration in my exams because we never knew how or when to apply for it, didn't know I was eligible, and weren't even informed that it existed until after the deadline for said application had already passed.
I have always wanted to be a vet. I had my whole life planned out, in terms of my education; do well in my GCSE's, study A-Level Biology and Chemistry, and apply to VetMed. Of course, it didn't work out like that. Instead, I've ended up with subpar grades in my GCSEs, three A-Levels that don't link to each other at all, and studying a course I can't bring myself to enjoy whatsoever because I know that this isn't where I'm supposed to be.
I feel like I'm never going to be happy because I'm never going to be a vet. I was dealt a *****y hand, and didn't know how to deal with it in a way that wouldn't ruin everything I had been wanting and working for. I genuinely cannot envision a life where I'm satisfied with who I am and what I've achieved because I'll never meet the goal I was aiming for this entire time. I've been telling myself that I enjoy this course, that I'll be happy working one of the jobs it could lead to, that it's not that bad; but I can't convince myself of any of it, because in the back of my mind, I'll always know I'm lying.
It's so stupid. Why am I 18 years old and laying in bed every night, wishing I could start my life again? Feeling like it's already over, when I've not even lived two decades of it yet?
It's so stupid. I'm so stupid. I hate this life.