I have had a high platelet count the past two months. what are causes of this?

High platelet: How high? Most common causes for high platelet count is reactive, reactive to infection, inflammation, or iron deficiency, etc. Bone marrow disorder (myeloproliferative disorder) is a common blood disorder leading to the persistent elevation in platelet count.

Primary or reactive: this elevation could be primary or autonomous hematologic disease i.e., part of myeloproliferative disorder ,or reactive secondary to inflammation ,infection