lumps on bottoms of feet

My 18 year old son has these lumps on the botton of his foot, they are almost like bubbles but they are in clusters. They have nothing inside of them, no blood, no infection but they seem to be multiplying and they are causing him horrible pain. He won't be able to walk before much longer. he asked me a few days ago to get a needle and get a splinter out from the bottom of his foot but hwen i looked at it they weren't splinters but these lumps that were hollow inside and there were about 15-20 lumps in one cluster and another cluster had about 9 lumps and another cluster had about 4-5 lumps. Do you know what these are and what we need to do to get rid of them? They are seriously hurting him!