I think you probably took your science classes a little to fast. You ought to start slow and add classes as you feel comfortable. You could retake some of your low grades (physics and chem) at a community college at a slower pace (part-time or maybe one at a time?).
Then, as you feel more comfortable and confident about science classes, you can take upper-division classes at a post-bacc university, preferably in biology. Add more classes per term as you get used to it.
Finally, study hard for the MCAT. Good luck!