Can someone tell me what this is ( graphic)

jay

It comes and go but I can feel it growing and when it does grow it goes into this boil and it hurts really bad like if I'm bending over something but then it'll go down Weeks later. I never have this until I was pregnant and I'm currently 19 weeks. When it does go into a boil it feels like a pimple what is that? And as you can see it's made it's own little dark spot