OK.. first off, these are good questions and you should be asking them of your teacher even before you ask them here.
I will try to give you some ideas and some critiques.. but ultimately the process and the solution has to be yours. Bonus points for asking the question tho.. that takes cajones.
Ok.. first some observations. You text too much. Waaay too much. It shows in the way that you write your letters and notes and that immediately degrades your grades or appearance. It may be a short cut for spelling, but it weakens the points you are trying to make.
Next. Mythology: There are plenty of alternate sources for the various stories and tales of greek and roman gods. THey are actually pretty good all things considered once you get into the stories. For example the Iliad (Achiles journey home after Troy) is a damned good story, and has been made into a few movies.
Sometimes people READ but they do not 'hear' the words. So comprehension is lost. Try this trick and read it out loud to someone who will patiently listen without comment. That sometimes forces you to make it make sense. (understand that part?). It starts hard and slow but it gets easier fast.
Look for alternate sources of the same material. Books-on-tape is a great example. Someone reads TO YOU and you need just to listen. I bet your comprehension goes higher in that technique.
Spend some extra time.. dig out those old tests and re-read the assignments for one or two.. can you see the points you missed and maybe understand why you missed them?
.. bottom line ... try a different approach. You need a different way to see your assigment. Go ask the teacher to help you get that after all its her job and she is prob. good at it even if she is a tough grader.