Even the most studious, accomplished college student has had that ONE class that absolutely kicked their butts. If you need this class for your major, seriously ask yourself if you can afford to drop it now and take it again another semester without it pushing out your graduation date (longer time in school = more money now + opportunity cost of not getting out into the work world when you planned). Then, get super serious about upping your time spent on this class, because what you are doing now (while it seems reasonable and may have worked in high school or for other college classes), clearly isn’t enough. That means accepting that you will be spending less time devoted to EC’s, socializing or to classes you are breezing through. In addition to going to office hours, see what on-campus study group/tutoring resources are available. Some schools have organized study groups for specific classes, or drop-in tutoring. This is rough, but you haven’t exhausted all of your possibilities yet - good luck.