Difficulties with exams
In my experience, if you're interested in joining a PhD program, as long as you're above the minimum required GPA they weigh your research experience, publications (if any) and recommendation letters much higher than your scores. If you want to find out whether you like academia and academia likes you back, find a professor willing to work with you on a research project or ask if one of their graduate students needs help with something. There are people who are great at both research and exams, but they are two very different skills IMO.


  Whenever I talk to graduate or PhD students or even professors, they
  always tell me that they have been straight A+ students.


Depending on the school, country and program, graduate courses are almost always straightforward to get very good grades in since they are largely literature and/or project based. Undergraduate programs tend to be harsher with grading and exams. I would wager that at least some of these academics you've spoken to don't remember their undergraduate scores exactly. :)