21yr f constant lower tummy pain! in c-section(2yrs old) more left side swollen feels like pressure! what could it be?

Many possibilities: Your question asks about a 21yo, but you list yourself as 25. I am assuming you are asking about you. Lower abdominal pain after c-section could be a hernia (may hurt more with positions, cough, sneeze, lift, and see a bulge), scar tissue inside abdomen, endometriosis, a growth on your left ovary, or an inflammatory bowel illness. See md and consider a ct scan of your abdomen. Good luck!