I am 7.5 years post RNY and I neither drink fruit juice nor do I drink with my meals!!!
If the coffee mate was NOT sugar free - that could have caused you to dump, the fruit juice could have caused you to dump and I'll bet you felt full after eating because of the juice too. I don't find that liquids flush food out of my pouch, but that it all backs up until I puke!
In short: no juice, no creamer unless it's sugar free, don't drink with meals. Nobody should be dumping at 13 days because you should be drinking water and eating protein at this stage!
Congrats on your surgery, BTW, my sister had her RNY in Essex in November 2010 and has done really well!
8 years + post RNY - 100% EWL and maintaining ...