Whispers in the abyss

So I have these whispers of doubts within myself internally and I know I shouldn’t have but I just do. Its in regards to how since I have been in graduate school, I haven’t really passed any tests, quizzes or major assignments with A’s and B’s. It has been mostly on the lines of C’s, D’s, and F’s, and its just so deflating because it makes me feel so deflated, like I don’t belong here or that there is something wrong with me. It’s almost like being back at the first college I went to my first two years of college. I did fine my first semester, and then I had these tragic family incidences that warped and turn my world upside down and I begin down this slippery slope of failing and struggling in a lot of my engineering classes until I finally decided to transfer to another school (where I ultimately got my bachelor’s degree). It’s like déjà vu, except this time around, I don’t really have any tragic incidences that is preventing me from being successful where I am at. I don’t know what’s wrong with me, but it makes me doubt my intelligence, my desire to learn, my spirit to be curious. I feel as if there is something about this school that is stifling me. I don’t know what it is, but I wish I knew so I could face it head on and take it out. But until then, I guess I will continue to be disappointed at the grades I earned while in graduate school and continue on this trail of wondering what is internally wrong with me. Its very frustrating because of how I feel being a minority in a program taking classes that had nothing to do with what I did as an undergrad and spending ridiculous amounts of time playing catch-up in classes by going back and researching and surfing and reading up to 4 or 5 subjects at a time per class I take (I average 3 classes a semester thus far) plus seeking a lot of help (especially in one of these classes I took last semester almost every other day with the professor). And I feel the said pattern is on assignments and take-home tests I put my blood, sweat, and tears to I fail worse than on said assignments in which I did not try or just did not care about. Its almost as if by me coming into the program I have came in, I am just simply setting myself up for failure. Now don’t get me wrong, I won't stop nor do I mind doing what I am doing in terms of researching and studying extra materials for classes but its like wow for me. I am also concern that it seems that I was successful at the school I transferred to which is an HBCU, and yet the first school I went to the engineering program was majority institution and now the school I am attending for graduate school is also majority institution. Does this mean that perhaps I am not cut out for these types of schools? That certainly can’t be a fact or a terrible notion to even entertain. So then why I am struggling so much academically, (and heck spiritually, socially, physically, and emotionally) at this school I am at now?Is it the school or is it me?