Hello. I'm glad you found us. If you've had periodic CBC's throughout your life, it's unlikely that you've had ITP your whole life. It would have been discovered on the CBC's. They check that also when you give blood and would have alerted you if counts were low. ITP is very easy to diagnose because it's based on a simple CBC. How odd that he would have said that, doesn't make sense. It doesn't really matter how long you've had it. People can go through life with lower than normal counts and never know it unless they have symptoms (bruises, petechiae, bleeding) or have a CBC. Since you had no symptoms, your counts were either in a safe range or your body was handling low counts well.
ITP can be triggered by many things. Medications, (including antibiotics), an illness, a supplement, a vaccine or any other toxin that you could have come in contact with. Some people never find the 'cause'.
There are quite a few other treatment options to try. It would be helpful for you to read the posts here to try to become familiar with the treatments before your appointment. Ask questions here if you need to. You can advocate for yourself and suggest treatments to your doctor; it's not a one-sided thing. 21k is a low count, but if your symptoms are minimal, your body is handling it.
