Welcome @meganpeters013, I don't have any experience with Hashimoto's but there are many members here on Connect with experience. I did see a Mayo Clinic Newsfeed post that may help answer your question:
-- Mayo Clinic Q and A: What causes a high platelet count?
https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-what-causes-a-high-platelet-count/
You might also want to scan through discussions by other members on Hashimoto's. Here's a link that lists the different discussions - https://connect.mayoclinic.org/search/discussions/.

When is your hematologist appointment?