Welcome to HCM.
You have taken Ortho Tri-Cyclen
Lo for several months.Now you presents with missed period without missing any pill.
Actually period starts within 7 days after ending hormonal
pill or starting with placebo pill.
So first of all,you do a home pregnancy
test for HCG to exclude pregnancy.Although,chance of pregnancy is very rare or negligible.
If test is negative,then need not to be worried.You can take the next pack as usual as per schedule.
It may be due to side effect of the contraceptive
pill, more likely it causes early or delayed period,irregular bleeding,nausea,vomiting
,headache,change in mood or psychological problem etc.
Always consult with your doctor regarding missed period if more than 7 days.