I agree if he stays constipated milk and milk products in large quanities is going to make it worse. Mine only get one glass a day and we don't drink milk we drink soy milk, it actually helps you go. Have you tried the flavored waters, mine drink the kool-aid brand and think it is kool-aid.
He is gagging when you give him something to try----so you let it go----that is the problem he knows you will let it go.
I don't have anything in fridge but fruit-soy milk-yogurt-kool aid water, fruit drinks(they make a new one that has serving of fruits and veggies in it) If we even buy cookies or junk food it it put up where they don't know it is and can't reach. If they don't eat atleast half of what is on their plate they don't get desert and they don't get anything to eat till next meal or snacktime. I have always done this with mine and they know not to fight about because that is one thing I don't give in on. I make 2 veggies and a meat for supper. They eat it or do without. If they eat only the meat and no veggies and want more meat they don't get it till they eat a few bites of each veggie on the plate. It works. My kids eat salads, carrots, corn, green beans, soup beans, most all meats except meatloaf.
You can also buy spagetti sauce that has veggies alreadt in it. Or shred and add veggies yourself to the foods you are making
Does he like any fruit? I'd keep trying different kinds--- strawberries and rasberries are usually well liked. If need be, put a tiny bit of sugar on top. My kids have always eaten lots of fruit---- but when my older son who is now 5 was constipated regularly--- we increased it. We also decreased his milk. Milk will fill a kid up and back a kid up at the same time. Then they don't want to eat food. My kids get more dairy from yogurt and cheese now. Don't get me wrong, they get milk every day---- but I don't let it be the main beverage. I also would consider not serving anything to drink at dinner time or if you do, serve just water. Kids sometimes will drink so much they aren't hungry. We also increased juice (and we only use 100% juice) for my constipated guy. Rarely has he had any problems since I became conscious of it.
I don't know what that powder was---- but I'm familiar with the "powerful pellets" as we called them. Good luck!!
you know I think this was old , stale and dried up it had been there days ....I dont think he just did it , maybe he had an accident and hid it, the only way is that it is old...so have some humor and laugh it off with him. Make sure he eats plenty as too many youngsters actually dont eat a quantity oif food ..plenty of water also , Stop the fighting with him let him be in control of his eating put plenty on his plate then leave him to get on with it.he could be reacting to your over reacting...Good Luck