Fullness in lower abdomen, fatigue and sore nipples. could i be pregnant?

Yes: If you are female, fertile, and fornicating. Otherwise, no.

Maybe: The answer to this question is easy to find. Either test with a reliable home urine pregnancy test (following the instructions) or have your physician perform a blood test. These symptoms could also be signs of a potentially more serious condition (such as ovarian disease) depending on your age and other risk factors. As always, when in doubt, seek the advice of a professional.