After i eat or use the bathroom the left lower part of my abdomen swells and i feel a bump. it is a pretty big bump i feel. could this be indicative of a hernia or a possible tumor?

Doctor can examine: A 25 year-old with this situation can see her primary care doctor for an exam, go home and poop everything out (may need laxative), and return for a second exam right away... and that should help the doctor decide what the bump is. Hopefully, there is a significance difference before and after the restroom, so it won't be hard for the doctor to figure it out. Otherwise, it might be more serious.