is there any other condition that could cause this?

Hi,
Welcome to ehealthforum,
There can be chances of spontaneous recanalization of the fallopian tubes after few years of ligation or due to slipping off of clips/ligatures/sutures etc. If the ovaries are functional and you had been having regular periods (usually an indication that you are having regular ovulation), the chances of pregnancy cannot be ruled out (especially if you are sexually active without use of birth control methods). The symptoms described by you do suggest possibility of pregnancy. Wait for your investigation results. Look for the blood HCG results (for accurate confirmation/ruling out of pregnancy). Consider getting serial HCG levels estimated if pregnancy is suspected. Doubling up of the hormone levels in 48-72 hours will show that pregnancy is going on smoothly. An ultrasound scan done will also help to confirm gestational age of fetus/baby and at the same time help to look for any other structural problems (ovarian cysts, enlarged uterus, uterine fibroids etc). Treatment as indicated by your examination findings/investigation results would be started to help you. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Take adequate rest. Drink plenty of water. Maintain healthy diet and lifestyle.
Take care.