Hi, I actually have the same issue as of last year. Never had it before and not sure why it’s happening now. Maybe my physiology has changed or the arch of my foot has dropped completely.
My podiatrist recommended buying custom insoles, not the over the counter stuff. As a temporary measure, she cut some thick foam pads to place it around the ball of my feet, so the ball actually doesn’t touch the bottom of the insoles. You can buy pre-cut foam pads like this: https://www.myfootshop.com/dancers-pads-premium-foam?gclid=Cj0KEQiAlsrFBRCAxcCB54XElLEBEiQA_ei0DFqOZ3UKIvY_K1w0xxEbMIz5RsWJao-8KE0eMEGuY3caAoyY8P8HAQ
They however will last for 2-3 weeks and I also tried buying dancer’s pad that stick to the top of my shoe insoles and cutting it to shape, but they don’t stick very well and I gave up. Neither is comfortable for running, but it’ll work maybe just enough for your half marathon.
As for the custom insole, I didn’t buy it from my podiatrist, because I’ve had bad experience getting them 10 years ago, and it was just a waste of money for no guaranteed benefit. The podiatrist is happy to charge me$300 for custom insoles, but won’t even bother to give me a 30 day satisfaction guarantee warranty. I ended up buying Hoka Infinite (discontinued but on clearance online) or buying Hoka Arahi. The cushioning in the shoe is J framed, means it’s slanted towards the side, so your feet ends up landing on a bit of an angle rather than on the balls. It has worked for me, but does take a month to get used to, which isn’t enough time for your half marathon.
