How can I treat pain in my tailbone because of my wheelchair?

Use a doughnut. There is an orthopedic appliance called a doughnut seat. It is literally shaped like a doughnut, which takes direct pressure off the tailbone. You can find these at most stores that carry medical supplies. Also, wearing a supportive pant, like biker's pants can be helpful.
Tailbone pain. See a doctor of osteopathy who does osteopathic manipulative therapy (omt) either full time, or within their practice otherwise. Ask them though, if they can do the specific treatment for coccyxgeal pain. There is a technique specific for this problem and it works well!