Ball of one foot sore under callus

I have been preparing for a hike early nest month and have walked 48 miles these past three weeks getting the body in shape. My regimen includes 4 miles without stopping averaging 3.2 mph every other day. Yesterday, the ball of one foot was noticeably sore, not pain, just a little sensitive under the callus. No blister on surface but obviously some friction irritation. Any suggestions for treatment? I only have a week to finish my regimen and have ten more pounds to add to the pack. I am hoping that if I give the foot a day or two of rest, the foot will be ok to continue without creating more concerning irritation. Also, what might have been the cause? In the last 48 miles I have had no foot or other physical problems. There were three things I did different and most likely one or a combinations of those changes was the culprit but I am not sure which was the most likely. New socks with a similar mix of wool, synthetic, and stretch fabric. New insoles, Spenco 5 replacing my old Spenco 4. And I added 4 more pounds bring my total load to 30 pounds. I am thinking the socks or the new slightly longer inserts are causing my problem. I can and have adjusted my Danner hiking boot laces as needed. Boots are broken in, supple, fit well and I have been using them for 15 years in the Alaska back country, but no long treks.

Does anyone have suggestions for dealing with the callus soreness so I can finish my preparations in a week or is that too unrealistic? Do you think a couple of days off the "track" will do the trick? Anyone have similar problems? I am not a novice backpacker, but have not prepared for extended hikes since I was 15 (now 67).

Lost Dutchman, you said "... have been using them for 15 years in the Alaska back country..."

I hope that's not the same set of boots you've had for all 15 years. ha ha

You might need to replace your insoles with some Superfeet insoles. Superfeet helped me carry an 80 lb pack in the Brooks Range for 9 days. I needed some cushion!

Also, ensure your feet aren't moving around at all. Causes might be socks that are too thin, boots that are too wide, or laces that aren't tight enough.

Possibly...your socks are too loose. I know this is the last idea presented but it's happened to me. I wore socks that moved around on me and it really irritated my foot. Beyong the utter annoyance, it rubbed like sandpaper.

are you putting in all this mileage walking on asphalt and/or cement whilist wearing your hiking boots?

Try to do your training walks on softer surfaces.

Do take the weekend off to let your feet rest and heal.

I'd put the old insoles back in - unless they're really trashed. What I suspect has happened is that your foot was used to the fairly hard sub-surface of the old, compressed insoles - and if there was any motion in the boot your foot slid OVER the old insoles.
Now the new ones are there - they're springy - and rather than sliding over the surface, your sock is sticking to the insole and the callous on your foot is sticking to the sock so you're pulling at the layer of skin underneath - causing pain.