So HotI, is it all in my head then?
I just pasted the info, i had a bub to attempt to get to sleep, and didn't have time to even read through it properly. There could be a few things going on, your son is 4 months which is often a time that parents report that sleep patterns change, bubs are unsettled, and/or their supply is dropping. Bub or you could be getting sick, or he could be heading for a growth spurt. It could be that the Mirena affects your supply, meds affect all of us differently. You could try boosting your supply through extra feeds and they try lactation cookies or some of the herbs etc that are meant to help. You could see if your supply picks up again after a few days or you could try to get the mirena out now.

i take meds that are reported to make breastfeeding difficult. i have to take the meds, and can't take meds to increase supply (cos they would counteract) so for me, from the begining i choose to feed often and as much as my DD would take. Luckily for me, she was happy to feed 2 hourly or less. I was able to avoid using any formula and we are still breastfeeding at 17 months and during pregnancy. I don't know whether the meds make breastfeeding difficult FOR ME, or whether even without the meds, we would have fallen into the same pattern of feeding. I just had to make decisions on the info that was out there, and what i was seeing with me and my bub.