Advice on bfing cycle

I've been breastfeeding my son for almost 14 months. AF came back at 8 months. My cycle had been 6 weeks or less since AF came back. This month I skipped altogether, but at 6 weeks I have a brown watery discharge for three days. At 8 weeks now and no sign of AF. Dollar store pregnancy tests are negative. Anyone else experience this? Doctor said not to worry until I miss three months, but something doesn't feel right.