Hi, thanks for the query.
Dark spotting for 2-3 days , pregnancy
test -ve , so remote chances of pregnancy.
All these troubles are most probably due to irritation , food poisoning
( mild degree) anxiety.
Over feeding is another reason for these things. Last reason may be due to some gastritis
Gastritis may be due to fried food over eating , smoking alcohol etc.
Good luck .Dr. HET.