My 2 week old son started off on the breast but...

My 2 week old son started off on the breast but with not succeding we switched to formula. The hospital was using the NAN formula so i have kept him on that which i did use for my 1st as well, but over the last 2 days he has become very constipated and throwing up some if not all of his bottle. I have an appointment with the family nurse lady but was just seeing if anyone has gone through this and if there are any hints of good formulas that may help with this. Would appreciate the feedback. Cheers Jacqui