I feel mentally slow and worthless.

Hi there. So I will begin by mentioning some facts about me. I'm a 17 years old girl soon to turn 18, living in Eastern Europe and studying at one of the best highschools from the capital. I'm also at the most challenging but not impossible profile, namely mathematics and computer sciences. Although life in middle school wasn't neither very simple nor extremely complicated, I realize now that the discrepancy between middle school and highschool is strikingly higher that I expected and that I have several lacunae in comparison with other classmates. I have to mention aswell that I never intended to choose this profile as is not at all chiming with my inner self. However, my father somehow convinced me into choosing math because he is a physics teacher and wanted me to form a logical thinking. To his disappointment, I can't seem to excel on these subjects regarding mathematics, physics, chemistry and computer science and it's now too late to transfer myself at another profile; that and also I don't want to accept the fact that maybe I'm not a clever person, at least an intelligent one. I didn't want to believe that I was mentally challenged maybe? Unfortunately I find myself giving credence more and more to the idea that maybe I am stupid. I always asociated not being good in subjects as specified above with being stupid. I also need to say that I am very lazy and I get bored and get demoralized way too easily. I might not have try harder and If I tried little and failed, I gave up. I just can't get past the idea that I maybe have to work harder than somebody else to be good at math because I'm not smart. I used to read many books in middle school and at the begining of highschool but now I'm becoming lazy on that matter too. Also I thought I was great at history and languages but being anxious, many times shy and always thinking of not failing and look stupid have driven me into not being able to speek properly in front of anybody, not being able to express myself as I do in writing. I sound retardet, without any solid arguments. So that's why most of the time I keep quiet even at the subjects I like, being afraid not to sound stupid. My self esteem has decreased significantly over the past 3-4 yeas. I don't consider myself a very happy person and a very accomplished one. I haven't achieved much in life hitherto and I'm not satisfied with the way things run in my life. I don't like to complain so I like to keep quiet about it most of the time although I must say, it's hard not having a shoulder to cry on. I also hate using this state of mind and soul of mine as an apology to my ignorance and indolence. I am the single one to blame for this negative and self-deprecating mood I've been dwelling on for months now. Belittling oneself can cause serious damage to ones soul so much that it starts projecting his fears into reality and influence the way he thinks about himself and the way others see him. I often find myself questioning weather if I just exaggerate or there is some truth hidden in my belief that I am indeed a lost cause but as I mentioned, regardless of that, this state of mind alone it's bad for me.
However, I can't deny some real aspects that on a certain degree affected me ( maybe not as much as I am telling now). I am weak.
I tend to be in a constant contradiction with myself and that adds up to my shitty self.
To get to the heart of the problem, I was recently evaluated orally by my physics teacher. I barely knew anything for that day's lesson. However, this doesn't bother me as much as calculus. I felt terrible stupid in front the backboard not being able to do some simple calculus and associations. I lost myself and also I blame my slow thinking because of my lack of practices and lacunea. In spite that, I surely would have solve those calculus on my notebook, not being pressure put on me, even though maybe a little bit slower than others but not as it was in front of the blackboard. Am i wrong?
Is it possible to be so stupid like me? So lazy? And worthless..I feel total ****. And I think I'm becoming depressed if I'm not already.