Started brushing teeth 3-4 times/day & rinsing with salt water. Getting canker sores a bit more often now. Can my change in oral hygiene cause this?

Perhaps. You may be overdoing it, traumatically injuring your soft tissues and your teeth. Please review your oral hygiene regimen with your Dentist or Hygienist who can evaluate it’s efficacy. For example, if you do not floss or WaterPik daily you greatly increase the chance of tooth loss due to gum disease. Please seek professional guidance. .