Well we had to switch my son's formula a few times for the same issue and each time we started a new formula he got constipated. I think it's just their systems trying to adjust. When we started soy formula though it was great and had no more problems with rashes, mucus and had less spit up. I have heard of proSobee and I don't much about it...is it just a soy formula or does it have other "powers"? I used the generic soy from Target and had zero problems with it. Just an FYI if you want to consider it b/c it's significanly less expensive and at only 7 weeks you have many more weeks of formula ahead! ;) Although, it's one more formula switch and probably more constipation, but I think it's worth it!