Pimple like bump appearing on butt,leg and recently back

I am sexually active and we dont use protection all the time but i am on the pill and my boyfriend was a virgin when we first had sex he even took a std test (Aid/Hiv etc..)but i wasnt a virgin and i only had sex with one person before and he was a virgin but he never took a test but we only had sex about 3 times all with protection. Recently I got a pimple-like bump very small then it got bigger as the days passed soon it got puss-filled and it popped on it own and bleed for about 3 days then healed over but left a dark area where it once been i first got it in between my leg but not my thigh area further up and then my boyfriend got it  2 but i didnt have sex during the time i had the bump or even before that then i got it on top of my leg again and then on my outer leg and he got his on his thigh and his butt and i got one on my back today. So i dont think its an STI/STD but ithought it was erythema nodosum  because that occurs sometimes when you are on birth control until my boyfriend got it too and i then i just got back to nothing again. Does anybody have an idea on what it is  if anybody has an idea please let me know. Also me and my boyfriend are going on monday to the dcotor to find out finally !

[CrazyNet]

Sounds like just plain pimples to me!

[lissalee]

Look up "hidradenitis suppurativa" and see if that explains anything its rare and not contages. Ask your Gyno my helped me. Good luck