RHS, I remember having trouble making this decision early on in my career. I soon realised that being in a metal tube for hours at high cabin altitude and with dry air really exaggerates any symptoms you may have. Its easy to make the mistake of waking up one morning thinking you feel better and then going to work only to realise you're not quite right. Its one thing feeling ok while sitting on the sofa at home but another making a stressful approach at the end of a long day at work. Therefore I now wait until I feel completely better before I go back to work, or I wait until I feel fine sat at home and then wait a day or two more. Nothing worse than flying with someone who complains they have a cold or who have trouble equalising their ear pressure.
If its just your ears that are blocked, pinch your nose and swallow. Your ears will pressurise. Now, can you clear them easily in one go by yawning? If no, don't fly.