Brown discharge

I am 4 weeks, 3 days with baby #2. I got a positive pregnancy test 11dpo and the line was light pink but very visible. I tested again at 14 Dpo and it showed positive right away.

I started having brown discharge today but it isn’t heavy or anything. Is this normal? I didn’t experience this with my first baby.

I did ride the assault bike this morning, so I am wondering if this caused it.

Thanks!