Firstly I will advise you to take up blood HCG test for confirming whether you are pregnant or not. Pregnancy can occur after tubal ligation if the procedure fails. The failure rates, the reason for failure and the timing of a failure all depend on the type of sterilization procedure and the skill of the surgeon performing the procedure. I would also advise you an early ultrasound to determine the location of the pregnancy since the chances of ectopic pregnancy are high after tubal ligation. Getting pregnant after tubal ligation is possible but requires additional surgery or procedures such as in vitro fertilization. It is best to consult an experienced gynecologist and discuss your concerns. Do write to me again.
Best wishes and take care!