Doubling up on birth control pills (and taking Plan B which is simply a heavier dose of hormones) can throw your menstrual cycle off schedule and this MAY be what is happening here.
Keep in mind, however, that taking a pregnancy test one or two days after missing a pill and having sex is useless in determining pregnancy. Conception may have taken place but until the fertilized egg actually implants into the uterus (generally 7 to 10 days after conception which takes place in the fallopian tubes) the body is unaware that conception has taken place.
About all you can do is wait for your menstrual period and if it does not come at least two weeks after missing that pill, you take another pregnancy test. Generally one remains covered against pregnancy if they miss one pill so pregnancy is rare...but not unheard of...missing one birth control pill.
A total hysterectomy is major surgery. It should not be entered into lightly. While it may have been over done in the past, many insurance companies require that certain less invasive steps be taken before the decision to surgically remove the uterus and ovaries. This is a good thing although I know the biopsy isn't much fun.
Keep in mind that if ONLY the uterus is removed (and not the ovaries) you will not go into instant menopause. It is the ovaries that produce hormones and if they remain they will continue to produce hormones until they would gradually slow and stop with aging normally.
Thus, you can discuss only removal of the uterus (if you wish) for removal of the fibroids while retaining your ovaries.
For what it's worth, I had a hysterectomy at age 47 but retained my ovaries and did not begin menopause until my late 50's.