Brown dishcharge before period?

I've been having dark brown stringy discharge for the past 3 to 4 days a few hours in between. I had sex and used withdrawal on 3/19 and I keep thinking I could be pregnant. My period is supposed to start Monday, but I'm irregular so I'm not completely sure. I've been very paranoid so I could really use some advice!  (I've asked this before but I forgot to add details?) thanks for any feedback!