My likker gets hotter over time.

[Prime83]

I did my first batch a few weeks ago. It was a basic sugar wash. I used 5lbs of white table sugar to 3TBS of bakers yeast to two gallons of water. After my initial run the product came out at about 140 proof. I proofed it further down to 90. However the longer it sets on my counter the hotter to the tongue it gets. It was once nice and smooth now it is like a fireball in my mouth. Can anyone please advise me on something I could have done or a possible cause?