Can I make this very clear?
SEX MUST NOT HURT! NOT EVER!
If it does hurt, change what you’re doing.
Just to be even clearer. I’m not talking about consensual pain, which some people like and are perfectly entitled to like. I’m not talking about what for some people is a turn on.
I’m talking about hurt, pain that feels off, pain that feels as if there’s something wrong.
First off, get a medical check-up in case there’s a problem that might be able to be treated medically.
Quite often though, it’s either mismatched genital size or having intercourse too soon.
When he’s too big
If the man has a long penis and the women has a short vagina, then positions where he’s going in deep will be painful. You need to experiment to find out what positions work for you as a couple. Generally you need positions where he can’t get in too deep. Some suggestions are:
Positions where she has her legs together and his are wider,
Avoid positions where her back is arched, such as deep doggie where her chest is low, try it in a bridge position with her back flat,
When she’s on top, face towards him rather than away from him.
When she’s not ready
If your genitals are well-matched in size and it still hurts, you may be moving to intercourse before she is ready. I've written a lot on this, so I won’t go over too much of that here. The important thing to remember is that you can tell when a woman is ready for intercourse: she’ll really want it. She’ll have a desire to invite the penis in.
The physiological signs that she is ready are: her outer labia are full and puffed up and she’s lubricating. (Additional lubricant can be used, as long as she does actually want intercourse and her lack of lubrication is not due to a lack of desire). Most important though, is her mental and emotional desire to have the penis inside her. If she thinks she “should” be or “ought to be” ready but she’s not, the sex could be painful.
Pushing through if there’s pain or discomfort, in the hope that it’ll get better, just won’t work.
Applying pressure to pain generally causes more pain. It’s much better to slow down and take your time to get her body receptive to penis in vagina activity.
Inserting the Penis
Different angles of inserting the penis can make a difference if there is some discomfort around the opening. If it’s sore at the back end of the vaginal opening make sure the insertion angles in from the top, so there’s no pressure or pulling on the sore area. Once he’s in, it may well be fine.
And very importantly, make the penis insertion slow and gentle. Be relaxed and focused on the feeling. Once the penis is fully in, rest there a moment or longer to allow her vagina to relax and accommodate the penis.
Honing Your Pelvic Floor Muscles
This is really important - both toning and relaxing. A well-honed vagina is more responsive; it can receive and relax. There is more information in other blogs, here and here, on how to do this. One additional, enjoyable activity to help here is for the woman to have the penis (or a dilator/dildo) inside her, and to slowly and rhythmically draw in and release out with her vagina, breathing in and out as she goes. Breathe in slowly and deeply as you tighten your vagina around the penis, then release the breath out and release the hold with your vagina. This needs to feel smooth and flowing. You can also do this while he is thrusting, starting with slow gentle thrusts - pushing out with the vagina with his inward thrust, inviting him in, then squeezing as he withdraws.
And always remember that there are plenty of other ways to enjoy sexual connection other than intercourse if the penis-in-vagina thing just isn’t working for you at that particular time.