My 2 month old won't poop on his own

Hello...I'm new here and a first time mom. My little boy was born 4 weeks early. He's 2 months now and was doing great until the last 2 weeks or so he has not been pooping on his own. He screams and cries but he can't get it out. We saw the pediatrician and he said it was okay to use a q-tip with some Vaseline to help move things along. If I do this, gas comes out first then comes the poop. He's not constipated. It's soft/normal. He's a happy baby again. I'm nervous he will get dependent on this. 2 weeks now and he won't go on his own. I called the ped the other day and explained to him again and he said to change his formula from Goodstart to Emfamil Nutramigen. I tried for 3 feedings and he hated it. Didn't work for the poop, he kept stopping to burp every 1/2 ounce, would spit it out or struggle to suck. It's pretty thick. I am now back on the Goodstart but he still won't poop without my help. I have been trying not to use this method but its so hard when he is screaming and I know I can help him in less than 5 minutes. Anyone else go through this? I could use some advice. Thanks