My dad's been dealing with a high fever and chills since a couple of days ago. His platelet count has been fluctuating, it was 41k two days ago, then went up to 47k yesterday, but today it's lowered again to 45k. Tests for Dengue and Malaria came back negative, so I'm worried about what else could be causing this low platelet count. How long do you think it might take for his platelets to go back to normal?