Is anyone out there have the same problems with...

Is anyone out there have the same problems with me? my DS is nearly 6 mths and recently doesn't want to take his formula, I have to force him to drink everytime and it seems not working for long term as he starts cry histerically these few day if I offered him formula, my breastmilk suppy is very low now...don't know what to do...any advise out there would be very appreciated, just for the info, I use the Nestle NAN HA1 formula and thinking to switch to Karicare Gold to see whether he wants to take it or not. Any advise??? Thanks