The first few times you have intercourse or experience v*ginal penetration, you may feel a small to moderate amount of pain at the entrance to the vagina. There can be some bleeding or no bleeding at all and both are normal.
However, once you begin to feel unbearable pain during s*x or the mere thought of s*x scares you, then there is an issue.
Here are a few reasons why:
1. Vaginismus
This is a common condition. It involves an involuntary spasm in the vaginal muscles, sometimes caused by fear of being hurt.
2. Vaginal or sexual infections
These conditions are common and include yeast infections. Sexually transmitted diseases may include genital warts, herpes sores, or other STDs.
3. Tightness in the vagina entrance.
Women have to be enormously aroused to be able to accommodate a man’s penis. It takes multiple orgasms usually, so your partner has to be very patient.
In some situations, size matters—if, for example, a male partner has a large penis and your vagina is small, you could experience pain. Keep in mind, though, that a woman’s body size is not related to size of her vagina.
4. Problems with the cervix (opening to the uterus)
In this case, the penis can reach the cervix at maximum penetration. So problems with the cervix (such as infections) can cause pain during deep penetration.
5. Injury to the vulva or vagina
These injuries may include a tear from childbirth or from a cut (episiotomy) made in the area of skin between the vagina and anus during labor.
6. Insufficient Lubrication
In most women, the wall of the vagina responds to arousal by producing a liquid that moistens the vagina and its entrance, making penetration easier. Sometimes there isn’t enough lubrication — you may need more time for stimulation, or you may be nervous or tense.
Insufficient lubrication can also be caused by lowered levels of estrogen, which can make vaginal tissue more fragile and affect the vaginal walls in such a way that less liquid is produced. (Fabwoman)