My mom is experiencing chronic pain in the abdomen (upper left side or in the center sometimes) that comes and goes. her stomach is also constantly bloated/swelled up, and she sometimes feels nauseous. what can be causing this? is cancer likely?

I would suggest that you ask if she is also constipated. There is possibility of cancer, however it is more likely that she just needs to adjust her diet to drink adequate fluid with more vegetables and fruit to improve regularity of bowel activities and reduce fecal stasis. Diet high in certain sugars may also cause the symptoms.

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. The description you provided is too vague to suggest a diagnosis. It would be prudent to see a doctor. Wish you and your mother good health!