In order to obtain a medical marijuana card, your condition must be on your state's list of qualifying conditions.
Your doctor, with whom you have an established relationship, would have to do an exam and verify to the state you have the condition. In most states that is the extent of doctor involvement, although there are some states where the doctor is actually the one who makes the recommendation for the MMJ card. In my state they merely verify the condition and a separate board issues the MMJ card. Of note, very few states - PA, NJ, NM, ND - issue MMJ cards for Anxiety. A few more states give doctors discretion to prescribe the card: CA, OK, MO. In still other states, like mine, Anxiety is not on the list, it is legal to grow and purchase "recreational" MJ, same stuff, you just don't need a card for it. There are strains of MJ that are energizing, which you would want to avoid with anxiety, and strains that are more relaxing even sedating. The terms sativa for energizing and indica for sedating are misnomers, but still widely used. There is a growing method I've used, which is waiting longer to harvest, in which some of the THC is converted to the more sedating CBN. Tricky to know exactly when this is, but I had good luck last year. Your local dispensary is well versed in all this. Look for a product with lower THC and higher CBN. THC is psychoactive; CBN is not. MJ is of huge benefit to me with respect to pain, anxiety, sleep, but if you're new to it, start very low (it comes in a variety of strengths) and go very slow (tiny baby dose) until you know how you'll react. I do this with any new med.