I woke up the other morning with two small red swellings on the bottom of my heel and one distinct blackish dot in the middle of each swell (two dots total, about 1/4 to 1/2 inch apart). The swelling area is smooth. The dots themselves feel hard. I only even noticed it because it hurt to walk on it. Seemed to itch at first, but not anymore. They are now just sensitive & painful to the touch. I soaked my foot in warm water & epsom salts last night, and then this morning I woke up to the dark spots having gotten bigger. Now they kind of look like blood blisters. I did not injure my foot before this suddenly appeared the other day. How do I know if what I have is an insect or spider bite or if it is a plantar wart or something else entirely?