Majored in STEM, but emphasis on the "T," so my undergrad major didn't have any chem or physics. Echoing the other posters, the learning curve was/is very steep as it was a whole new way I had to approach class. As a nontrad, we don't even have the advantage of recency to the material from high school many fellow classmates have which made the learning curve suck. I'm coming up on my last semester of class for my post bacc and I'd really recommend religious use of Youtube, (AK Lectures, Organic Chemistry Tutor, and Professor Dave) with a lot of time devoted to practice problems. Focus on the problems your professor assigns as ungraded hw as those will constitute the majority of your tests. Work hard, and you got this.
Do not be discouraged if you do poorly on one test, just don't let it be more than one. 6 classes done so far with 5's A and each one featured one poor exam score. Retool, reload, meet with the professor and make doing well in these classes your number one goal.