I read this book as a teenager in the early 1990s.  It was a paperback, but I don’t think it was a Harlequin.

Hero                     

• An American soldier/person of importance

 Heroine

• An American from an upstanding family who were sympathetic to the plight of the Native American Indians

 Location

• America

 Era         

• During a war – not sure which one, but it involved Native American Indians

 Main plot                           

• Hero and heroine marry in a traditional Native American Indian ceremony.
• Heroine is given a necklace with a carved wooden charm (I think a turtle) in lieu of a wedding ring.
• Heroine is kidnapped on her wedding night.  She suffers a head injury and gets amnesia and finds out she is pregnant while imprisoned.
• The hero finds her, but she does not recognise him.
• The hero claims her and they are married in a traditional Christian ceremony.
• Heroine gives birth to their child – a girl  – and regains her memory.

 Other plot twists

• Heroine’s brother is fighting in the war.  He secretly marries a Native American Indian known to the family.  Heroine’s brother is killed in the war, and his wife dies in childbirth, and the heroine cares for their child – a son named Andrew (I think) after his father (the heroine’s brother).
• One particularly gruesome scene where a preacher is tortured and burned.