If they haven't eaten in 2 weeks and one is lying on its side it sounds like you may want to take them back to p-co. This is not normal behavior (in my experience). The ph etc is OK and they should have hid for a day or two and been shy for a few more days but, by now, they should be clinging to something and fanning or sitting on the bottom and picking over the substrate. If they aren't, things are not going well.
Shrimp often molt soon after you get them and the one on its side may be having a molting that is going badly.
As you say, you have no idea what p-co did to them (or didn't do). If it is anything like my local one there is a new teenager in the fish department every couple of months, s(he) is probably well meaning but completely clueless. I've heard them tell people the most bizarre things -- they will frequently say things that are dead wrong. You only have to look in their tanks to see that they are capable of killing large numbers of the fish in their care. When I go into their fish department Dachau comes to mind.