Helppppp!!

Hi, so I currently missed my period and today marked my 41st day of my cycle. I have been freaking out and this afternoon I had a dark brown discharge and don't quite know what's going on. I'm not on birth control and have had unprotected sex a couple times in the past month. I have taken 4 test all coming back negative. I've researched a lot just kind of want some advice! Thank you in advance!