Pregnancy test!!!

How soon can you take a pregnancy test? My SO and I recently decided to ttc we've been trying every other day and today I feel very tired and I keep having pains in the right lower part of my stomach where my ovary is and up behind my ribs on the right side. Also I'm having a lot more discharge than normal and have had a headache which I never get! my fertile week ended 3-4 days ago.