Does the world need another graphic designer?

Hi all! Could really use some advice & this seems to be the place.

Currently: I manage the "back end" of a retail store & do all the social media & light design work for our small business (among seemingly a million other things). I'm almost 27 and graduated in 2013 with a BA in Arts Management and a BA in Art History and have kind of taught myself what little I know (photoshop, some indesign, lightroom, etc).

I'm ready to move on from my current job, and am pretty sure graphic design is the right path for me. The question is: what's the best way to get into it?

I've been wanting to go back to school as I found my Arts Management degree too broad and am not interested in pursuing Art History as a career. And since I always told myself that I'd go to abroad if I were ever to further my education, I'd like to study in London (where I have lived before although I'm now home in New Jersey). I just can't decide what's best: certificate program, graduate program, or going back for another undergrad degree. I also took a quick peek at Shillington's program, but it seems a little unrealistic to be able to learn all there is to know about graphic design in a 3 or even 9 month course. I also have read quite a bit about self-teaching, but I think I'd prefer the structure and guidance that something more formal could provide.

If anyone has any advice on the above, I'd be so appreciative! I've really been struggling with what to do in my life lately. I always assumed I'd find my passion and everything would click, but here I am, still waiting. Anyone else feel like they're interested in too many things?