a brownish mucos like substance?

Hi,
Welcome to ehealthforum,
If you have missed your Depo shot, and had been having regular periods, then it would indicate regular and periodic ovulation (egg release from ovary). The brown discharge and your symptoms (brown discharge, increased appetite, increased tiredness, frequent urination, abdominal distension) could be suggestive of early pregnancy. Urine pregnancy tests usually start showing positive results late after about a week from missing periods. Sometimes they can also show you false negative results and hence cannot be relied upon for accuracy. Urine pregnancy test kits are calibrated ones, so they show positive results only after the hormonal levels in urine have reached a certain level. Blood/serum HCG level test are accurate and can detect pregnancy earlier than urine test.
You should consider visiting your gynecologist/obstetrician at the earliest for examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately).
Take care.