If your son hadn’t put on any weight or grown for 6 months, I think you would be right to be concerned but 6 weeks is not really long enough to worry about, especially if his blood work is all good.  I am willing to bet your little lad will be back on track again by his next appointment as all kids grow in fits and starts and the last 6 weeks have probably just been one of those normal  ’fits’!  If he didn’t have CAH, I am sure no-one would have even noticed or been concerned about it.