My 1 month old has extreme issues with constipation, I don't know what else to do! Please help?

My son is one month old. He has had trouble with constipation since day 1. He hardly ever goes to the bathroom on his own. He doesn't go for a while and I can tell he's in pain and trying to push but nothing is coming out. I then have to insert a thermometer into his rectum and pump his legs and push on his stomach for the poop to come out and when it does it is very hard and he strains to go. I have tried giving him pear juice, Karo syrup in milk and water, just plain water, water with anise, and infant suppositories. I have also tries adding more water to his formula. I have switches from similac to similac sensitive and am now trying Enfamil gentlease. He does not really seem to want to drink the gentlease. It's takes me forever to get him to drink a 4 oz bottle where as he would drink Te similar in minutes. I dont know what else to do! He is awake all day and most of the night grunting and fussing. Neither of us are sleeping and it's beggining to take a toll on me :(. I have also tried warm baths. He farts alot but no poop. Do you think there could be something wrong with his belly? Have you had an experience where your baby did not like the formula? What should I do, pleaseeeee help me. The Doctor keeps telling me it's normal but I know in my heart it is not. He does not have occasional constipation, he is like this all the time. Thanks