If your abuser has injured you, by all means try to get medical help. If your abuser goes with you to the doctor or emergency room, it may not be safe to tell the truth about what happened. But, try to find an opportunity to speak to the medical practitioner alone and where your abuser will not hear. Let the medical practitioner know what happened to you and see if it can be safely included in the medical record.
If it is safe and possible to do so, ask the medical practitioner to photograph your injuries, and to keep any evidence such as torn or bloody clothing with the medical record.
Be aware that if you see a doctor and your medical insurance policy is in your abuser's name - both your medical records and the fact that you've seen a doctor may be provided to your abuser. Discuss this with a domestic violence service provider.
If you do not need, or want, to go to an emergency room or doctor, have a friend photograph any bruises or cuts. Date the photograph and hide it in a safe place.