Constipated 2 1/2 week old?

Ok so I posted on here a couple days ago cause my LO is not pooping 2-3 times a day. He’s pooped twice in the last 4 days. Yesterday’s poop was dark green and really pasty looking. It eventually got more lose and had a yellow color in it so I thought that he had gotten most of it out and we should be golden from here on out. Not the case. He hasn’t pooped since and I can tell it’s still bothering him as he’s super fussy, but he’s still passing gas. So far ive tried the rectal thermometer, Vaseline on a q-tip, and kyro syrup in his formula. I don’t want to do the thermometer or q-tip too much as I don’t want him to become reliant on me so is there anything else I can do or give him? We switched his formula from enfamil newborn to gentlease about a week and a half ago, should I try switching again? Any help is very much appreciated!