Right after I had my catheter placed, I had to be very careful. The chiro did everything while I was on my back. Now that I've healed, I can lay on my stomach for an adjustment. As for the pinching you felt, it sounds like your catheter shifted. Mine used to lay right on my uterus and would made drains feel like childbirth, but now it is on the left and higher, so I get more gentle cramps in my intestines when I drain. If you still feel discomfort, you should lie down and try to get it to shift again...
and of course, tell your nurse.