I had that problem as, well and I've only been with one person my husband and after 8 1/2 years I had that. My gyo. Did and ultrasound on me and found out that I had varicose veins on my uterus. so maybe it's something you can look into.
we use plenty of lube and i usually am relaxed until i start to feel the pain, also, I do kegels a lot and we don't use condoms
Experiment with different water based lubricants. For me, I need at least one climax before intercourse. That will relax you and your muscles.
You can also buy a small toy. Your partner can use this to get you ready.
Remember to do your kiegel exercises. Squeeze. Release. Act as if the release is peeing. The squeeze is stop peeing. Do these exercises every day, for now, not during sex. You will see the differences after about a month.
Also. Latex free condoms IMO are better. Many people are sensitive to latex hope this helps! Maxy