I don't know why I am getting 1-2 bumps a day on my skin?

[mwemsmsdnd]

Hi there,
I have been getting red bumps for the past few weeks (at my parents home, at my own home afterwards). At first it was only around the hip back area, then I got one bump behind my knee, one at the side of breast, one under my eye etc. They are never really cluttered, but happen in different parts of body. After 2 days, they develop a white top, which makes it look like a pimple. When they go, they leave a purple mark. They are not itchy, more sore to touch. My skin feels itchy, however, not all the time (sometimes where it is itchy, I see a bump in the new few hours). I have been to 2 dermatologists, they don't know what it is. I did get a large tattoo several weeks ago and I did fly on the plane next day, wonder if this could be some bacterial infection like staph? Yesterday my boyfriend got few of these dots, whatever it is, seems contagious. Could you please shed some light on this? Thanks!