We were using ready mixed aptimel formula in hospital (long story but baby wouldn't latch). I've switched to powdered version since we came home and my LO has been Really constipated and in pain. We gave him water, massaged his tummy, warm baths, cycling with his feet and swapped back to the ready mixed formula. He seems to be ok now. But I've got a full box of powder. Will I be able to gradually wean him back onto the powder or am I stuck paying through the nose for the ready mixed?