My prefix will despite a fact, My infix will negatively react

Question

• My prefix will despite a fact
• My suffix tells what to do instead
• My infix will negatively react
• My whole is an idea in your head

Answer 1

I think the answer is

Thought

My prefix will despite a fact

Though = "despite the fact that"

My suffix tells what to do instead

Ought = "used to indicate duty or correctness"

My infix will negatively react

Ugh = "exclamation used to express disgust or horror"

My whole is an idea in your head

Thought = "an idea or opinion produced by thinking, or occurring suddenly in the mind"