Dear An: The three most common causes for a period that is almost two weeks late are:
1. Pregnancy--You mentioned that you have had three negative urine tests (hopefully including one that was done seven days after your missed flow). Usually that rules out a current pregnancy unless you conceived and are going to miscarry. It is hard to know why your other pregnancies were not detected until 8 weeks. Given this fact you might merit a blood pregnancy test.
2. MIssed/late ovulation---As you may know, in a normal cycle, estrogen is produced all month. Estrogen is responsible for building up the lining of your uterus so you have something to shed each month. In a normal cycle, progesterone production increases following ovulation. Progesterone "stabilizes" the uterine lining in preparation for a possible implantation of a new pregnancy. If you are not pregnant that month the levels of estrogen and progesterone fall, triggering the release of the uterine lining—your period.
So, if you do not ovulate, the estrogen build up of the lining continues, but without the usual ovulation associated progesterone. Thus, the hormone levels don't decline, and the lining stays up inside the uterus—your missed/late period.
Bilateral breast tenderness can be a very early sign of pregnancy, appearing as early as two weeks after conception. This is thought to be related to increasing levels of hormones such as estrogen. In a month without an ovulation, not only can a menstrual period be missed, but there can be breast tenderness as well. This is similar to the increased breast tenderness experienced by some women when first taking postmenopausal hormone therapy.
If all pregnancy tests are negative this would be my best GUESS since you had a history of irregular cycles in the past.
3. Sudden onset of menopause--This would be the most rare culprit. But if your cycles do not return an evaluation would include blood work to rule out menopause.
Bottom line, you really should see your GYN or even your local county family planning clinic. They can retest for pregnancy and if negative assess for other causes of your hot flashes and nausea.
Best wishes for conceiving promptly.
Yours,
Jane