Brown discharge-worried

I'm 19 weeks tomorrow. I had a good amount of brown discharge last night in my underwear before bed. First time seeing anything like this. I had a small spot of brown this morning after wiping after peeing. I'm calling the doctor this morning but they don't open for another 30 minutes. I'm not sure if this is "normal" or what would even cause it. My hubby and I haven't had sex in a week or so, so I'm sure it's not that. Has anyone else experienced this? Have you talked to your OB about it? Should I be worried? I'm feeling baby move everyday.