Bumps on the bottom of my feet

I have these lil bumps, they almost look like a pimple or a blister but they are under my skin on the bottom of my feet. I’ve never had them. I tried to pop one to see if it was a wart or something but it was kind of like a hard calus under the skin. what are they? I had one… now I have like 3 & they are really tender.