7 week old twins and feeding issues - spitting up, gas, constipation?

My 7 week old twins began having feeding issues a few weeks ago. I was feeeding them both while only adding a few Enfacare supplements here and there. They seemed to be doing well. Then a few weeks ago they began to get horribly gy. They both grunt like crazy and seem to be in pain when they p gas or try to have a bowel movement. Along with this they began spitting up a lot - but about an hour or 2 after feedings. They'd just be sleeping and wake up choking on spit up. I decided to try to switch to just Enfacare formula this week to see what happens. The giness has improved dramatically. The spitting up is not as bad. It's a smaller amount and is happening less frequently than with milk. However, it is still happening about once a day for each of the twins. It comes out their noses and it doesn't happen when they burp after a feeding. It's 1-2 hours after they eat. Have any other parents experienced this? I plan to talk to the pediatrician at their next checkup in a week, but wondered if there might be a better formula to try. Also - they seem to be constipated with the Enfamil Enfacare - their stools are less frequent and are a more formed stool as opposed to the runny milk stools. Is there a formula out there that would help with both the spit up and reduce constipation?