First, you have to make sure you're not allergic to oregano. If you are you should know already but it doesn't hurt to check if you for some reason don't know and have never tried oregano in any form.

Sinus headaches, sinus infections and head colds are frequently just a mould infection of the nasal passages. Even if you have a cold or some sort of fever that involve a nasal problem that's driving you berserk, this works better than anything else you can do. These infestations and infections can be quite debilitating sometimes.

Just boil some water - it has to be at a rolling boil - then pour it into a mug into which you've placed 2 to 4 drops of oregano oil into it. Snort it hard as you can, one nostril at a time (block the other one), deeply and repeatedly until it hurts and you just can't stand it any more. Now do the other nostril. Do this until you just can't any more.

Do this three to five times a day. You'll feel better within minutes, and if it goes away in a day or two (as it often does) you may have had a mould infection; all too common but seldom diagnosed properly.