For the past year and a half I have been suffering from severe sinus headaches. I've noticed that they often come after it rains or while it's raining. It is by far the most miserable thing I've ever felt. I take OTC nasal decongestant medicine and it does not seem to help as much. I also take Claratin-D and notice a difference there, but it does not fully go away until the next day it seems. I have not had any allergy tests, but what could it be that I'm allergic to? Is there something that I can do to prevent the headaches all together?
The nasal decongestant medications (especially if it's a nasal spray) and the "D" (also a decongestant) in the Claritin-D may be giving you re-bound headaches. I know it's really difficult, but decongestants should only be used for a short period of time. When they wear off, your symptoms come back worse than before.
Try using a Netty pot, saline spray, or those tablets that dissolve in the shower and release eucalyptus and mint. A hot shower may also clear your sinuses. Once the decongestants are out of your system, you may actually feel a lot better because you've broken the rebound cycle. Give it a couple of weeks.
If your symptoms persist, go to your doctor. You may need a prescription allergy medication or a nasal spray (not a otc decongestant one). Personally, I've found that a combination of the two works rather well.
The allergy tests are good to either avoid what you are allergic to (or in my case, find that I cannot really avoid what I am allergic to--dust, grass, outdoor mold). They are also useful if you want to go on and get the allergy shots. I wouldn't consider those until you find out if different medication will work.
Also, try switching to hypoallergenic or at least mild products, such as soaps, detergents, lotions, cleaning products.
I hope you feel better. And remember to only use oral decongestants when you really really need them and only for a couple of days. Avoid decongestant nasal sprays all together. They're just too addictive.