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If you are having bleeding after sex and have painful sex then you need to evaluate for your problem.Common causes can be lack of lubrication for which you can use a K-Y jelly
for lubrication and other causes can be small interoitus;cervical erosion;endometrosis;pelvic inflammation.Since you have been to Gynaec and even did a ultrasound
the pelvic causes are ruled out.So there is maximum chance that you have an ulcer on cervix
or cervical erosion which is cause of pain and bleeding during sex
.Please get internally examined by the Gynaec and she/he will treat you accordingly.