For About 3 Weeks Now Ive Been Having This On

For about 3 weeks now Ive been having this on and off brown discharge and sometimes it'll be brown or a black jelly like discharge coming out. It's been happening since I had sex three weeks ago and no i'm not pregnant but I have yet to get my period, over the last year my periods been irregular so i'm not sure what to expect. I also have redness on my perineum and it gets sore out of no where. Could it be an std or can it be because my period is irregular?