Hello,
Tubal ligation, regardless of whether the tubes are cut, burned, clipped, banded, or tied, is about 99 percent effective. The tubes have evolved in such a way as to try to heal themselves (like when the ends are cut and sutured,they may rejoin after sutures dissolve), and sometimes a tract(mostly endometriosis) develops that allows egg and sperm to meet.Hence there is an increased risk of having an ectopic pregnancy.
Hence to confirm the status of pregnancy, I suggest you to test for pregnancy by a highly sensitive pregnancy test 10 days post ovulation with a sensitive ( 20 - 25 mIU ) pregnancy test. Also then I would suggest you to get your serum HCG levels estimated since this is more specific than urine for pregnancy tests.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I'm not a doctor, but it is very possible that the tubal ligation didn't take. My sister had hers done and had to have them re-done because it didn't work the first time. Anyway, I'd suggest taking a pregnancy test, if it's negative see your doctor if you are still having those symptoms