Calculus is very heavily dependent upon precalculus and trigonometry. Thus how you are doing in this class probably depends upon how you did in those previous classes.
The first thing that comes to mind is to drop one class and take a W, then concentrate and work very hard on the classes that you have left. You can make up a missing class over the summer. Also, the majority of university students in the US take more than 4 years to graduate in any case, so taking one less class at a time and just taking an extra semester or two is not unusual. I would be inclined to drop the most difficult class. Chemistry and Biology at the same time sound like a lot to me.
Having had 8 months off between schools should not hurt you. I took two years off between schools and was a much better student when I returned, and this is not unusual.