My dad had a spine surgery about three weeks ago & since then he has been vomiting, he had a stomach pain and stomach bloated and has been constipated?

This may be due to: Pain post op, less mobility post op, use of narcotic medication postop or even an ileus residual post op (bowels not fully functioning). If he had an approach thru the abdomen, this is more likely. However, a gastritis or an ulcer can also be triggered from stress of surgery & so can a gallbladder attack. He may also be dehydrating so see your surgeon. There are also several other possibilities.

Post op abdomen: Most commonly this bloating and constipation is caused by narcotic pain medications. The treatment is laxatives or stool softeners or stopping the narcotics. Contact the surgeons office or your doctor to make sure he is cared for appropriately.