Not much later. Â I did have a terrible let-down, plus a baby that had a hard time with "suction" (prob. overbite). Â She HATED the let-down and would scream and scream and choke and gag, and, due to other issues, we started nursing lying down (warning: babies can get hooked on this position!) Â It helped a lot with the let down. Â Completely eliminated that trouble. Â
   Another issue could be possible allergies, which for us added to the mounting JOYS of nursing (I am being sarcastic) at about 2 months.  Screaming before, at the beginning, middle and after nursing, plus red bottom and mucousy stools.  I was a bit thickheaded, and didn't think of allergies, probably because nursing was ALWAYS difficult with her.  It was only on retrospect when I pinned down when it started.
   At first, I would narrow it down to your let down, gas, etc.  There are many ways you can avoid your monster let-down to test this out.  Pumping a minute first, popping him off for the let-down (clean diaper to soak up) , lying down during the let-down.  Could heavy let-down might also be connected to an EI after a cold?  If you can't narrow down the culprit and the problem doesn't subside as he gets older, it might be an allergy.  (Does he nurse more easily when drowsy and at night?  That's not a definitive sign by itself, but it is one symptom.  Pain receptors are sleepy then, too.)  Try eliminating your dairy intake first, if you suspect.  It seems the moms i talk to have luck with this alone.
   GOOD LUCK!