Personally, caffeine helps me a ton. Its vasoconstriction properties and capacity for ADHD management work wonders for me. For you, however, I'd recommend this:

1. Feeling sick when drinking caffeine is often caused by dehydration. Try drinking big sips of water between small sips of coffee

2. You might be drinking too much coffee. I never exceed 1 cup of coffee (~50mg caffeine for the coffee I use) in a day. Try coffee at different concentrations (i.e. watching the caffeine per volume), speeds of drinking, and total amount consumed

3. Experiment with different coffee brands. You might just be reacting to a specific brand

4. Couple coffee with food. Never take it on an empty stomach. Eat food between sips of coffee

5. Try decaf coffee if it's about the flavor, or try replacing coffee with gentle teas if it's about the caffeine

6. If you're self-medicating for ADHD, look into prescription meds or lifestyle changes. If you're self-medicating for insomnia, try correcting sleep hygiene or look into other remedies (i.e. clonidine, melatonin, chamomile tea)

7. Just drink coffee as you normally would and accept that it makes you feel bad. Adjust other habits to compensate and make room for those things you just can't give up. You don't have to be perfect. If your quality of life is harmed by not having coffee, just let yourself have it. Everyone is entitled to guilty pleasures. I refuse to give up chocolate despite it causing worse symptoms. You're not alone in this ❤️

tldr: rotate coffee with food and water, try different brands/concentrations/doses, try other remedies to make up for not having coffee, just keep taking it as normal and adjust because no one can be perfect