I have the Mirena and never noticed a drop in supply but that does not mean it doesn't happen to some people.
That said i wouldn't be rushing to get it removed, he could be fussing for many different reasons hun, it could all be a coincidence.

I'd suggest drinking plenty of water, using your lactation cookies and offering the boob as suggested by the ABA.
IF it continues and your REALLY worried about the affects it's having on you both then i would contact your GP and disvuss the options.
My Mirena had to be inserted at the local hosp with an OBGYN, the waiting list was quite long and the costs to see him and pay for the Mirena would stop me having it removed without reason.

I hope it's nothing, could he be teething (my girls started teething that early), wonder weeks ???

GL hun.