congrats for trying to breastfeed! im sorry it didnt work out.
you were actually right on by following your instincts to give soy. it really sounds like your son might have an allergy to milk. :( this is very very common.
also, when on formula, dr william sears recommends some water every day to counteract the strong concentration of formula. so you might want to try that.
dr can tell you whatever he wants to, but in the end YOUR instincts are the ones that matter. you can even lie to him about the formula you use if that helps, or find a doc who will support your decisions. some hospitols and doctors are paid to support a certain fomula.... so you have to watch it.. trust your instincts! THAT IS THE KEY! FOLLOW YOUR INSTINCTS, they are never wrong!
by the way, milk is a huge issue anyway... i recently learned that animal proteins are NOT good for us like the milk and meat industry would have us believe, they actually turn to an acid in our bodies and that causes osteoperosis! so if you want to never give cows milk to your son, dont! :D follow your instincts! and by the way, almond milk is great for boys, soy for girls. (after you are done with formula)
but... if you go back to breastfeeding (check, sometimes the milk doesnt stop for MONTHS after stopping nursing...) its free, and perfectly created for your baby. if you dont, formula comes in all shapes and sizes (for lack of better terms) and there is one that will work for your son!
ps when you start solids (which isnt until 4-6 months old or later) you can add a little milled flax for constipation. this is good, and healthy, and it isnt a problem if you have to give it every day to ward off constipation. just a pinch is probably fine for a small baby... but anyway, flax is fiber, and fiber absorbs water in the stomach, then is passed into the intesting, keeping the stool soft and moist, which makes babys stool much easier to pass and less constipation. this can be done even in adults with constipation. just sprinkle flax on your food once or twice a day, and let the fiber work the magic it was made to work! its GREAT!
good luck!