story-identification: fantasy story with physically weak protagonist that took place after nuclear winter

Question

I started reading this book when I was in either elementary school or middle school (anywhere from like 2004-2011) that I recall was too boring for me then but that I'm very interested in remembering now. Unfortunately I don't remember much about the book except these key details:

• I think it was written in the first person
• The main character was a boy/young man who was physically weak, too weak to be a knight, but was actually very skilled in military strategy
• He might have had asthma?
• The fantasy world they lived in was cold because it was actually Earth in the aftermath of a nuclear winter - this knowledge was not revealed at the end but was part of the book's exposition and not considered that big of a deal
• The main character might have been attending some sort of knighthood school or something in the beginning
• There may not have been any magic in this setting (but also there might have been and I don't remember)
• Eventually he has to go out on some sort of quest, but he is insecure about his poor physical prowess
• He had some sort of female friend who supported him
• The book cover was some sort of landscape that was mostly green and grey
• I don't think it was high fantasy - as far as I know, humans were the only race present

Sorry this is so incredibly vague! I've been racking my brain about this for hours now and can't seem to find it anywhere.

Answer 1

This sounds to me like Tomorrow's Magic, originally published as two volumes, Winter of Magic's Return and Tomorrow's Magic.

Not first person, but most of the other points check out based on my own memory and the Kindle sample:

• Main character is Wellington "Welly" Jones, overweight and with poor eyesight.
• Vision and weight issues prevented Welly from attending the Cardiff Military Academy; as it is he is getting a general education at Llandoylan School.
• The Devastation 500 years before is discussed in the first chapter; the words "nuclear war" are used.
• There is magic in the setting, but that is not clear to the characters early on--if you didn't finish the book, you may not have seen much of it.
• Along with his best friend Heather and a boy who claims to be Merlin, Welly goes on a quest to find and bring back King Arthur.
• The cover shown on Goodreads includes a fair amount of green and grey.
• There may be some magical creatures lurking around the edges (it's been 30+ years since I read it myself), but the focus is definitely on humans.