Welcome to HCM.Pregnancy
is possible if intercourse is done around ovulation time in regular cycle.
Now you are presented with irregular bleeding with different color and twice in month.
It may be due to early implantation
leading to miscarriage
.Also you have stomach pain and vomiting
Do a USG pelvis and consult with gynecologist with report.
Be well and practice safe sex in future to avoid unwanted pregnancy.