Unpredictable Eating

[novelleo]

I got my current baby corn snake on 11/27/2019.
Disc: I'm young and fairly new to this, but I've been trying my best so please forgive if I add unnecessary details here and there, I'm not entirely sure what is/isn't relevant.
Background:
When I first got him, he took pinkie mice weekly without much of an issue. Prior to shedding, he refused food, but I had heard that was normal, so I didn't think much of it. He had his first shed 1/5/2020 (17.5 inches long) and his second shed on 3/27/2020 (18.5) and, by that time, he would still only take 1 pinkie per week, other than once when he took two. Around then, it started becoming normal for him to refuse to eat the first time I'd offer (still on a weekly basis), but typically took it the second time (I'd wait ~2 days before offering again). I thought it might be because I started giving him 2 pinkies instead of 1, so I didn't worry. His longest hunger strike was 14 days long and ended 4/22 (but, again, that was after I fed him 2 large pinkies so I didn't think anything of it). Since then, he's only taken 1 pinkie mouse. He's currently on day 10 of denying food, but he doesn't look like he's about to shed. He also doesn't look underweight to me, so I'm really confused.
I keep reading articles saying that he should be over 20 inches by now and taking 3 pinkies a week, but I can barely get him to take 1. He gets defensive and/or just ignores it and slithers away. I've fed him in his enclosure since I got him, but I've tried leaving it in there and walking away when he refuses. He just doesn't show interest.
Also, I don't currently have the resources to buy urine to scent food.
I'm maintaining the rest of his husbandry to the standards that have been expressed to me (20 gallon tank for right now that will be upgraded at least to a 40 gallon when he grows up, 2 hides, substrate he can burrow in, water dish in a corner with clean water that's deep enough for him to submerge himself in, regular spot cleaning, ~80 degree warm side, and regular handling). I just want to have a happy, healthy snake. If there's something that I can do to fix or improve this, please let me know. Thank you!!!