Hello, Thank you for writing to us, Pain after sex might be there so nothing to more worry about it. But as i had gone through your query i found you point out there that it was stomach pain and lower back pain since you had sex. so, If its been already long time the would like to suggest you that its time to concern a good doctor. other possibility for pain is if amount of pre cum from vagina is less as you mentioned you are 64 years old and due to that wetness it might possible to having internal injury and pain is there. if its because of less pre cum from vagina You may use lubricant if it happens each time you had sex so that penis could enter easily. Or you should use different positions in which penis enters easily. I would also suggest to go for foreplay and Oral sex first before you go for intercourse because it will help for pre cum and also you and your partner will have more pleasure than normal intercourse. Still you are facing the same issue i would like to suggest to concern a good doctor and check for issue they will suggest you better. Hope you will find it helpful. Thanks & Regards, Dr. Gaurav Prajapat