When should i worry about a pang in the abdomen, like a pain, mostly on the left side? i've been feeling it sometimes today but i don't know if its serious or not?

There isn't enough description of your symptom for us to make a differential diagnosis for you. Persistent abdominal discomfort, especially if there's associated abdominal tenderness, warrants an examination by a physician. Diverticulitis, inflammatory bowel disease, pelvic inflammatory disease, inguinal hernia are some causes of left sided abdominal pain. Get examined if pain persists.