I would ask how old/big is he?
2-3 mice every 2-3 weeks is a very unusual feeding schedule. 3 prey at a time is generally seen as a big regurge risk (the mice start decaying faster than the snake can digest them) and needing 2 at a time either means you're probably overfeeding (if it's an adult snake) or you're feeding too small of prey items (feeding hoppers when he should be on adult mice for example).
1 proper sized mouse every 14-21 days is a valid maintenance diet for an adult, but not for a hatchling.
Hatchlings should start off at about every 5 days or so, and move up in feeding days as the size of the prey gets increased.
And regardless of size/schedule, it's generally accepted that you should just leave them alone once you notice them going into shed phase (typically when they go blue you know for certain although some keepers can tell earlier than that, I can't) until after the shed is finished. A missed feeding schedule during shed times won't hurt them and you minimize other potential issues like regurges. Plus some just won't even take the food during a shed cycle.