Damn Chemistry! in Work/School issues/accopmlishments

I am pretty frustrated right now in my chemistry class. I believe it's going to be the death of me. I started crying during our second class when the teacher told us that math conversions are the foundation of chemistry. I was so confused and I can't bare the thought of failing this class.
The more classes we had since then I have gained confidence. I understand the concepts of a lot of things, but those conversions are still rough for me.
I did the wrong homework for yesterdays class which meant that I had to use last pm to do the homework that was due yesterday. It took me hours... literally. It really was a weeks worth of homework in one night. That meant that I couldn't finish the reading that was due for today. I Given that I didn't finish the reading, todays lecture was a waste. I have been reading since I came home but I suspect that had I done the reading first, it would have been much more clear to me today. Now we have a test on Saturday so there really is no time for me to absorb this stuff.
I also really don't know how any of this shit is going to help me in my career! I freaking hate this class. Also, I have been in a shitty mood for the majority of the day. I don't know if it's because of all this or not or if my frustration is a result of my negative feelings today.