Brown discharge at 13 weeks

Starting about 3 or 4 days ago I noticed when I wipe there’s a brown discharge. It’s not like old blood, it honestly looks dirty but I definitely clean down there. There’s also some in my panties but I’ve noticed discharge in my panties even before I became pregnant and I’m stuck only fitting in my period panties so there’s already some stains so it’s hard to tell old from new. Last Tuesday I went to the doctor and I seen the baby, heartbeat was 150. Even though I just seen the baby and know it’s okay I can’t help but worry that this brown discharge is something more. My mom keeps trying to reassure me that it’s normal but I’m a worry wart. Has anyone else experienced this and everything been okay? Is this normal?