oh yeah been there done that!! I have two boys as well, and my youngest had struggled with this for months and I stayed up nights trying to find a way to help him
First try to remove as much dairy as possible. No apple juice, no carrots for starters. Give him prune juice, pear juice, peaches..Think "P". then try to get him to have some WHOLE grains, oatmeal, Brown rice, flaxseed( which you can also grind up and put in his food). This is a lifestyle for a while. Get used to it. I have heard lots of different ideas but I try to stick to the natural remedies but here are some others too: dark corn syrup, benefiber, miralax. But I would try all others first , you can get drops at the health food store just ask for baby constipation drops. They work. Tea especially senna tea. Just a little, don't over do it on him his belly is sensitive so don't shock his system all at once I would try the prune juice first and OJ is good too. Lots of water. His bowels have to be re trained and you don't want him in pain where he avoids bowel movents then you will have a much bigger problem. I also made some cookies, These worked well. I used oatmeal, whole wheat flour, ground flax and some whole flax seeds, raisins, dried apricots cut up into bits and any other dried fruit you like,currants, dried cranberries etc.. brown sugar or organic sugar,honey if you want but they suggest no honey for kids under two due to spores but you can try agave sugar or the dark corn syrup, or just stick with the brown. you can add some dark chocolate chips too and basically anything else... Make them as if you would oatmeal raisin..follow that basic recipe. These are a yummy treat and filled with FIBER. That will help him. If he still drinks out of a bottle try putting some pureed baby food in there. PRUNES , pears , peaches mix with his milk I know you can't avoid milk all together but you can also supplement with almond milk, rice milk, hemp milk, yogurt is also good, it has essential bacterias that can aid in his digestion etc.. keep soy to a minimum. You can also add some baby cereal with warm water in his bottle shake to dissolve it then add his milk or do a combo, cereal (WHOLE grain oatmeal, WHOLE grain brown rice) then fruit puree and then top off with milk so he will drink it. I also would add some olive oil to his diet. I hope these things help. Please remember to read the labels. Try to keep his food WHOLE foods, no preservatives, no corn syrup, NO food DYES!, LOOK for whole grains, If you give him just rice cereal or white flour you are defeating the purpose. Fruit, veggies,squash are good too, leafy greens etc.. Whole grain bread. Maybe try some toast and things like that... Good Luck I know how frustrating it can be and how much we want to take the pain away..