Tired Lungs and ballooned legs

Not sure if anybody’s had this … I’ve been doing a block hard build phase, the plan has been pretty hard (plus all the extra riding I’ve been doing) that a 3+1 is way too ambitious for me and I’ve settled on a 2+1 kind of cycle.

The reason why I know that I need a 2+1 cycle was that when I try to do hard threshold workouts on the 3rd build week according to plan, my lungs felt like they couldn’t process enough air and lactate builds up way too quickly for the given intensity. And my legs in general just felt like they were going to explode on and off the bike. Then i know i need to take it easy for the week.

Has anybody run into similar situations? I guess this is half observation and half question.