Weird period???

So my period is about 2 weeks late, I'm not pregnant because I haven't had sex in a couple months. I just had surgery and I've been really stressed lately which is why, I'm assuming, it's late. Today I had some spotting but it's like a dark brown paste. Should I be concerned about this? I sometimes have a little bit of brownish blood at the end but this is like the color and consistency of mud. Help!