Excessive salivation doesn't cause headaches. However, headaches together with speech problem may be caused by malocclusion of upper and lower jaws or teeth - i.e. coordination problems or imbalance in the jaws and teeth. Kindly visit an Orthodontist and they can check if your headaches and speech problems are related to any dental or jaw issue.
Next Steps
Visit an Orthodontist to check for discrepancy in upper and lower jaw coordination.