If it were me, I would take the pass/fail. Based on what you mentioned about motivation and the level of classes you are taking, (you are still taking entry level science classes), the B's, especially weighted with 5 credit hours, could wreck your GPA. There is a good chance that your level of motivation will lead you to get additional bad grades in science courses.
So, my academic prescription for you would be:
A) Have a come to Jesus moment now and turn your attitude around regarding your academic motivation.
B) Take the pass/fails in the course you will get a B in.
C) Never take a pass/fail again
D) With your renewed mindset related to your study habits, absolutely crush all of your other classes.
What you need to understand is that (if you are serious about becoming a Dr.) learning the sciences must become second nature to you and you need to be able to absorb the material, retain it long-term and look forward to learning new material for the rest of your life. As a Dr., studying the sciences is a way of life and for your patients sake, you must be good at it.