I posted this in another summer course plan thread:
My first summer semester, I took gen chem 2 (lab required with the course) and precalc 1. B's in both (my CC didn't offer +/-). Last summer I took Bio 2 and was forced to take an additional class (American history 2) I didn't need (stupid way the GI bill law is written) - A's in both. It's not bad if you dedicate time to it. This coming summer, I have "completely lost my mind" (as my advisor so eloquently put it), and will be taking both ochem labs, genetics, literature, and a computer science class (the latter 2 should be ver easy and the CS class has no recitation in the summer). It works out to be a 13 credit summer over 2 six week periods. My issue is that I am working against time in that I am trying to finish before my GI Bill runs out on me. This will be after I write the DAT in May.
So, OP, while it is certainly doable, especially if you have no job, spouse or offspring (all of which I have), it won't be easy. Take heart in knowing you're not alone. My advisor said to thinking it as a warmup for dental school.