Sobriety question.

Had a beer tonight after 45 days sober. Been a drinker every night for the past 15 years. I don’t plan on drinking again anytime soon.

Since I’ve quit I’ve felt absolutely terrible. Exhausted, brain fog and just down. I’ve heard it takes 3-12 months for your brain to heal.

My question is did I set the timeline back to day one? Also what do you do to feel somewhat normal after quitting?