I read your post and re-read it before replying. I have been at this over 17 years but I still remember the anxiety of being a student and the fear of failing regardless. I remember the "what ifs" and being terrified, especially when my personal life interfered..death and divorce. I remember how hard it was so I hope this helps:
First, let me say that the fact that you haven't quit is in itself admirable. Each time you see something that you have seen before strengthens your knowledge and expertise.
Don't allow the "should have beens" thoughts into your heart. That only beats you down and makes you discouraged. You've been hit alot and now it's time to show your strength. I'll bet that there is something in the curriculum that you are especially good at. When you are feeling discouraged, remind yourself of your strengths, not weaknesses. Acknowledge the weakness, and face it head on.
I am not sure how you study, but if I may share what has helped me: Record all lectures (with permission of your Instructor), get a headset to attach to the recorder later and play it while you drive, clean house, cook, going to sleep, etc. Highlight in your text in colors to emphasize what is most important. A friend of mine and I made "flashcards" out of notecard and markers with terms and names of certain types of bacteria, etc. and tested one another.
When you start to get overwhelmed, walk away for 20 min, eat, drink, go back to study. Don't allow the phone to ring, tv on, anyone in the room while you study. If there is background noise, turn on a fan and concentrate on what you need to get the job done.
When you take your board again, go with the first answer, and don't go back and second guess yourself.
Set the same time daily aside to go over your notes and tapes. If you have a family to take care of, enlist others to help while you study. Let the laundry go, turn your underwear inside out, order Pizza and eat a banana!
And last, but not least, remember that dehydrated cells get sleepy and over hydrated ones get agitated. Drink your water, get plenty of rest. And if you can exercise it will take off some of the stress.
God bless you and your efforts, Dear. You'll make it....!