When i was a young child i put an old thermometer in the microwave and it exploded. could i be at risk of mercury poisoning ten years later?

Maybe: It doesn't take much mercury to be toxic. If you ate any food that was prepared in the microwave, no telling how much methylmercury you've consumed. I recommend you see a physician member of the American College for Advancement in Medicine (ACAM) or International College of Integrative Medicine (ICIM) for evaluation for treatment. I would use a combination of oral DMSA and IV or oral EDTA.