I was a bit like you... struggled at university, failed plenty of topics (some twice) because it never "clicked". I fluked a job at a small company and turns out I'm pretty decent with people & understanding what people want/need. I got by with my code, but it was elementary if I'm honest with myself.

For the past 14 years I've run my own web dev company but I understood my limitations and hired people who are actually good at coding and I've stuck to what I'm good at.

From what you write, there doesn't appear to be a passion for coding - avoiding assignments & now struggling with core constructs point to that. But something at some point got you into this field - perhaps there's something to the side that might suit your skills/passion more? Testing, QA, project management, client management, business analysis... there's lots of roles that benefit of understanding programming concepts that don't rely on you actually being a gun programmer.