First of all, you should undergo blood test
for beta hCG and TVS scan (around 4 weeks) to confirm or exclude intrauterine pregnancy as early home pregnancy test may give false negative result.
Brown vaginal discharge
with late period seems to more likely implantation
bleeding or sign of miscarriage
In exclusion of conceptional product, other reasons of light spotting are hormonal imbalance, stress/ anxiety, thyroid problem, wt gain/extreme loss, irregular eating habits etc.
Do some investigations to rule out underlying pathology like USG lower abdomen, Thyroid profile, other hormonal assay, blood sugar etc. So consult with your doctor and take suggestive measures.
Avoid stress, take healthy diet, control body wt and need proper sleep. Sore breast is due to progesterone
hormone. Use tight breast support for discomfort and take prime rose cap.
If you need further consultation with me, then you can visit http://www.healthcaremagic.com/doctors/dr-soumen-patra/63326.
Be well & take care.