Help with Graduate School?

 I am currently a senior getting my Undergrad from Stony Brook U. I have decided recently during my last year here that I do want to attend Grad school after thinking that was a dream of mine from the past. I refuse to be told that it is "too late" because I know that is far from the truth.. So firsthand, if you're here to feed me words of the like, please kindly take your impish remarks elsewhere where they may be warranted. Thank you. 

 I am a major of Sociology, but I am interested in obtaining my Masters of Social Work through my current University. My question is.. My GPA unfortunately has suffered here because I have changed my major probably as much as I have my socks. Before transferring to SBU I had a GPA ranging somewhere between 3.7 - 3.9, now I've dropped down to just below the cusp of consideration for the MSW program, which is 2.5. Not mentioning numbers here to dwell on what happened previously, as that is only a place of reference, not residence.. Just listing them to show the true gravity of the situation. My question is.. Do Grad schools within the University you're already attending consider you just because you've already invested so much at that particular school? While my GPA has tanked to put it nicely, it was previously outstanding, which shows that I am indeed capable. A GRE score is not needed for entrance into this specific program, so I don't have that assent unfortunately. However, as an undergrad I did take a 500 level (Graduate) course at got an A.. which my professor said was remarkable and admirable considering my age & limited academic experience compared to my colleagues.  My issue is that, coming from my previous school I was enrolled in an honors program with VERY intimate courses (10 students at best) & now I'm here in 200+ lecture hall courses.. I really suffered extreme culture shock. I am hoping that through my graduate professor I can obtain a supportive letter of recommendation to strengthen my acceptance ability.. Does this sound at all plausible? 

 Lastly, can one become a professor with a MSW? This is a field I do express interest in outside of additional interests. I love teaching & helping others and I really love college. (No, I do not mean that at all immaturely, I do not even remotely fit the bill of what society calls a 'college student' outside of the classroom). I was just curious. If not, what route does one take in becoming a professor? Can you become a professor of Psychology without a major in the field? While I do major in the neighboring academia of Sociology, I do have a very strong concentration in Psychology & this was my first major at my current University. I am not even 100% sure of what exactly I want to "do" when I "grow up" but I love school & it is more or less who I wholeheartedly am.

Thank you in advance.