School Troubles

I could just cry! I feel so confused and disillusioned.
I just wanted to become a better human being and help others.And all a long, the Lord most certainly has been faithful to grow me, stretch me and use me. And then I come to these walls and here I am freaking out! The fact that I freak out might actually be more frustrating.
"What are you talking about?", you ask... The answer: Biochemistry... it looms over me and waits til I'm down to kick me repeatedly and aggressively.

I am more and more aware of how stupid I am every time I go to class. I just don't get it. It makes me angry, because I really wish I did. I really wish I understood the Vmax of the Mk of the enzyme inhibitors but I don't even know how to calculate the Vmax.. Actually, I didn't even know enzymes had velocity.
And outside of feeling irreversibly dumb, incompetent and overall like a big failure on a regular basis, the fact is I have to pass this class with a C or I do not get my Biology minor which I have tortured myself working for the last 4 years.
Now here I am questioning my entire life. What was I thinking? Maybe I am not cut out to be a college student or a nurse. What am I doing? Am I wasting my life? Why couldn't I have just gone to school to be a teacher or been naturally talented to do some vocation that's awesome..
On the other hand, doesn't that mostly mean I am asking God if He really knows what He's doing? And if He really is in control of this and if He actually hates me?
That's certainly not my place! I am such a mess. I need a hug and a lot more of Jesus and probably a really patient and smart biochemistry tutor since my first test is a week from today.
I know not everything is smooth sailing. I know this semester is a ridiculously minuscule percentage of life.  And I know God is in control and He loves me even though I fail in many levels and areas.
...what to do now...