This happens sometimes and could happen for a number of reasons such as not enough lubrication in the vagina, the position, your emotions, or it could be cause by an infection. If penetrative sex hurts, either stop or try some different things (e.g. use lube or change position). Talk to you partner about what feels good for you. If you are worried or penetrative sex is consistently painful, speak to a doctor or nurse. Find out more about painful sex