Lactic acid is NOT related to exercise-induced DOMS. Get that in your head!!!
There have been countless tests and researched that showed this.
1) The downhill tests in the 80s. They measured lactate in a large group of people before and during a 45-min treadmill run, one time at flat elevation and one time at -10% elevation (sub 5 pace, so decent runners). In the flat group, lactate was rising dramatically to 5+ mmol. In the downhill group, lactate remained low at 1-1.5 mmol. It's very easy to run quickly on a downhill treadmill due to gravity. HOWEVER, in terms of DOMS/muscle soreness following 72 hours after the test, the flat group, despite producing lots of lactate and working much harder had no fatigue, whereas the downhill group that did an relatively easy effort had substantial soreness.
2) Dr. Bruce Gladden, expert on lactate, muscle physiology and kinesiology stated:
"For much of the 20th century, lactate was largely considered a dead-end waste product of glycolysis due to hypoxia, the primary cause of the O2 debt following exercise, a major cause of muscle fatigue, and a key factor in acidosis-induced tissue damage. Since the 1970s, a 'lactate revolution' has occurred…… It now appears that increased lactate production and concentration as a result of anoxia or dysoxia (hypoxia) are often the exception rather than the rule. Lactic acidosis is being re-evaluated as a factor in muscle fatigue….Lactate can no longer be considered the usual suspect for metabolic 'crimes', but is instead a central player in cellular, regional and whole body metabolism……"
What you describe is much more likely to be dehydration or glycogen depletion. Did you significantly increase your water intake and carb intake after you started training so much more and harder? It could also be that you are simply training way above your current level. The race will show, GL but please don't become another blamer of lactate, it's not the evil thing anymore people thought it to be in the 60s and early 70s.