If you had a tubal ligation...you're probably not pregnant. take a home pregnancy test if you are concerned. It's probably something else ... are you gaining weight? Maybe that's causing you to feel the stretch.
The only way to know for certain if you are pregnant is to do a HPT or have a bloodtest done. You are causing yourself needless worry about an ectopic, without even knowing your pregnant yet. Good luck to you!
only thing to do is test. have you gained any weight recently? i had a tummy tuck and when i went up even 2-3 pounds i felt that stretching. you are supposed to keep your weight steady. (even knowing that, i got pregnant once after the tuck, had a m/c and i am still trying!).