Having stomach pain and i feel it is rigid like simething in it. i had abdominal ultrasound and dr said all ok. can this be cancer?

Unlikely at 33: You might ask about an egd and let somebody take a real look.

Unlikely: If you mean stomach as in the organ in which the food goes an ultrasound is not the best way to look at it and a referral to a GI doc for possible upper endoscopy could be considered. If you mean the abdomen (the area in which the stomach, liver are) the ultrasound is reasonable but does not see the colon well and a GI consult for colonoscopy may be indicated. Statistically though it is unlikely.