Most novelists working full-time jobs finish their manuscripts by writing less frequently but more deliberately - quality over volume. The exhaustion you're hitting after two years is real, and it often means you're trying to squeeze too much into those weekend blocks when your brain is already fried. What tends to work better is accepting that some weeks you'll write nothing, and other weeks you might get three solid sessions in, rather than forcing yourself into a rigid weekend routine.
The shift that actually helps is treating writing like a habit you protect in small pockets rather than a project you schedule. If you can grab 15 minutes on a Tuesday after work before scrolling, that consistency adds up more than a frustrated Saturday where you stare at the page for an hour. I know that sounds counterintuitive when you're trying to finish something, but the people I know who actually completed novels while working were the ones who stopped viewing it as "time stolen from rest" and started seeing those small daily moments as the real progress. Two years of effort is genuinely substantial - you're not failing because you haven't finished yet, you're just working at the pace that fits your actual life right now.
One practical thing: track what you write, not how long you write. Even 500 words three times a week gets you 78,000 words in a year. That number stops feeling impossible when you're measuring it week to week instead of staring at how far you still have to go. The novel won't finish because you powered through on willpower alone - it finishes because you showed up consistently enough that it became part of your routine, not an obligation fighting against your exhaustion.