Alex! Good to see you post again.
A former co-worker of mine had the same experience. He usually had two very large coffees in the morning, and another one before lunch, so perhaps 8 to 10 normal ācupsā overall. In his early 50s, obese, nearly officially diabetic according to his doctor.
He was prejudiced against beef and pork, somewhat, for whatever reasons. He went to eating mostly fish and chicken, all seafood and poultry really, and he did eat eggs, lots of eggs. Very successful for him - he lost 20kg / 40+lbs in less than half a year, health markers inproved. He did say that coffee made him feel funny, like there was a tension in him, slightly vibrating all over, not a good sensation.
He too changed to tea, overall consumption went down, but he never felt 100% satisfied - in the end he settled on a mix of tea and coffee, but only 1 or 2 or 3 regular cups. It was a clear-cut thing for him, though, he said - his new diet made him sensitive to caffeine, he was sure.
My mother - always a āstandardā diet eater - said that as she got older, her caffeine sensitivity went up a lot. I believe itās fairly-well established that many of us feel moreso as we age; we tend to clear the caffeine from our bodies more slowly.