the history typically suggests an implantation bleed but as your dark brown bleed coincides with the menstrual due date. it may have been scanty menses as well. now as you have done the urine pregnancy test after 7 days post missed periods and it was negative it does rule out pregnancy. as you feel that you may still be pregnant the best way is the blood serum beta hcg test (human chorionic gonadotropin) which can be done to allay your doubt. if the beta hcg levels are more than 1 then the pregnancy is confirmed. else if it is less than 1 then it is ruled out completely. the symptoms you are experiencing can be safe attributed to premenstrual syndrome if the test is negative. premenstrual syndrome mimics early pregnancy symptoms like headache nausea sore breasts mild cramps and increased frequency of urination. this may indicate that you may resume your menses in a few days if the beta hcg is negative as well. for further doubts consult an obstetrician and gynaecologist online --> <link>
how to confirm my pregnancy?