Hello and thanks for your query.
I shall make an effort to provide you with good professional recommendations specific to your questions.
The nauseas feeling after sex is usually caused by either a
hormonal imbalance, or from the
cervix being hit continuously during sex.
The hormonal imbalance can be caused by taking a hormonal
contraception pill, or it can be just a natural imbalance.
Try asking your partner to not thrust so hard, or penetrate so deeply and see if there is an improvement.
Because you have said that you are on the pill, I would expect a hormonal imbalance to be the culprit. I would suggest seeing your doctor to rule out this and also for considering different pills if required.
Yet again, I duly appreciate your query to me, I do hope that have found something useful to help you and I shall be glad to answer any further apprehensions.
Sincerely,