Own Worst Grammatical Issue

Spelling hands down is my biggest grammatical issue. I never have been very good at spelling since elementary school, and never worked on it. My main issue with this is my vocabulary is far more well rounded in comparison to my spelling. I can use a word but hardly spell it. Sometime the spelling is so wrong that spell check has no idea what I'm trying to type. A close second for grammatical issues is comma usage. I go with what i feel and that's hardly ever right.