I've been e periencing this recently. Was tryng to clear some blocked ducts by hand expression after using an Avent single manual pump.
After pumping, I feel fine. But after I have used fingers to express and massage ESP the aerola area to clear the last remaining drops of milk, I feel somewhat mini contractions at my nipples (even the one that wasn't hand expressed).

This is followed by body shivers. I am suspecting it is because I'm running a fever now but I find it odd that i was ok (no shivering) after pumping but this happens after I hand express.

Could it be that I used too much strength to squeeze?
Sometmes it worsens to full body uncontrollable shivers, just like when I was sufferng frm breast infection and terrible engorgement. The pain makes my whole body shiver.