If the ovaries and tubes are still there,very remote possibility that the sperms migrated through the vault of vagina and you got pregnant and if it is 23 weeks it has to be abdominal pregnancy
as the pregnancy in the tubes or ovary cannot last for more than 6-8 weeks.
Other possibility is a mass in the ovary which could have rose your hcg
levels get a sonography
done and meet your doctor. Don't worry every thing would be fine.