I can't remember if you commuted last year or if you've just started a new one...
Yeah, commuting seems to knock it out of you a lot more than weekend long rides. Seems to be something to do with the lack of proper recovery time. You ride reasonably strenuously in the morning, short break, rinse and repeat in the evening. Probably don't stretch. Your overnight break is pretty much the same and isn't really long enough to properly recover from the day. You DO need to make sure you get enough calories in as well, otherwise you're way in deficit by the end of the week and feel awful. Bonking on your way home on a Friday when you've not eaten enough during the week is just the worst feeling. You'll need a lot more calories than makes sense, too, and I don't know why this is.
But you do harden up to it in time.
indeed... I consume around 3.5k/day ! but I also go to gym so that adds extra burn/stress to my body!
but I think it's the short spurts on the bike that ruin me.
I jam my backpack full of stuff to a point that my shoulders hurt at the end of the commute... BUT I STILL RIDE IT!!! GOTTA KEEP PUSHING