Dear Stephanie,
quite abit can be going on with you that is causing all these symptoms.
Here are possible causes to your symptoms other than pregnancy.
Loss of menstruation could be due to exessive weight gain or loss, fatigue, hormonal problems, tension and stress. Also tubal sterilization can be associated with irregular menstrual bleeding.
The sore breast could be due to hormonal imbalance, birth control and impending menstruation
The nausea could be due to food poisoning, stress and stomach disorders.
The headachs could be due to dehydration, caffeine withdrawl, impending menstruation and eye strain.
Now for the bad news, since you have had a tubal ligation your chances has increased for an ectopic pregnancy. In an ectopic pregnancy the egg implants in areas other than the uterus, when that happends your body does not produce the correct hCG levels to support the pregnancy because it is in the wrong place. Since the hCG levels are lower than normal in a ectopic pregnancy it may not be detectable by a home pregnancy test. I strongly suggest you see your doctor right away to rule out an ectopic pregnancy they are fatal within hours after rupture. SO PLEASE SEE YOUR DOCTOR!
Hoping everything is fine,
Love Falon