Unfortunately, finding out if you are "officially" dyslexic, when you left school long ago, isn't always easy. -You must be assessed by a psychologist who is recognized by your workplace or college, or whom you are referred to by a reputable organization (like the disability office of your local college or the dyslexia association). The assessment is not inexpensive. Your health insurance may cover all or some of the costs. If you attend college and paid for mandatory insurance through that college, some psychologists' fees are covered by that insurance, but you will have to check around.
It should be easier, shouldn't it!