Welcome!!! The transition from the Standard American Diet (SAD) is really hard for people like us who have been eating grains for years. You are going to experience what is called "carb flu", this will entail headaches, drowsiness, irritation, etc.... lenth of duration depends from person to person. Mine was about 2 weeks long, now I feel great. I think you should go slow in your transition. First, cut out all of the processed, sugary stuff that you eat. Replace grains with quinoa, a seed that acts like a grain, into your main meals. Going full throtle on day 1 is not always the best way to go about this. Take it day by day and eventually you will get there.
If you need support, we're all here for rooting for you!