Either cancel, or prepare to go on the trip with a cold.
You'll want some non-drowsy cold/flu tablets. They usually contain ibuprofen/paracetamol, so they'll reduce any pain, and they usually contain a decongestant, so your nose isn't stuffy.
Then consider some cough drops.
But, keep an eye on it. If you've been sick for 2 days already, you may feel better by Thursday.