invisilbe sweeling on soles of feet

Suddenly last night when I walked it felt like there was a swollen area on my right foot below the third and fourth toes that hurt when I put pressure on it. it was gone this morning but this afternoon I have the same thing on my left foot at the inner arch immediately above the heel. It feels exactly like a lump but when I look nothing is there. It hurts unbearable to walk and was not there at all even one hour ago. The skin and general apprearance of both feet look normal. The only other thing is that occasionally they start itching unbearably for a few minutes. Again nothing is visible to the eye. What could this be? I hesitate to go to the doctor since it may well disappear by the time I get to his office.