This afternoon I walked out to get my mail and as soon as I walked outside my head felt heavy and had pressure. I thought to myself,well it cant be pollen cause it rained half an inch last night. Then I look on TWC and it says today is a very high pollen day. How is that possible when my area got heavy rain last night?

they don't go out and measure the pollen in every place, the pollen forecast is based on what is in season where. It doesn't take rain into account. Rain does help a lot with pollen, but not all. Your head could have also felt pressure from the change in the atmospheric pressure after the front moved through.

Rain increases mold growth, so if you're allergic to mold, you can feel worse.

Kev,

If you'd gone outside right after the rain, within an hour or so, the pollen load would have been lighter. The 'washing' effect of raindrops scavenging pollen from the air is overcome by the next pollen release, typically heaviest during morning sun.

And of course, as W.Chic has suggested, mold has a party after a heavy rain ...

Best wishes.