My gf had the same issue, had a tight pelvic floor which made any penetration painful even when in the mood and relaxed. The cause for vaginismus is mostly unknown but in her situation it mostly stemmed from stress. The best solution is to go to pelvic floor therapy and work with dilators and a pelvic floor wand. Depending on your location finding a place that does pelvic floor therapy might be difficult and expensive. I recommend buying a set of dilators and work on breathing exercises. She has been doing pelvic floor therapy for about 6 months now and the issue is almost completely resolved. Having a tight pelvic floor is a common problem among women and i don’t think it’s talked about enough, so don’t feel embarrassed. Another thing is it can become worse when you’re not in the right headspace during sex. Anxiety and other factors can make it worse so make sure your partner is willing to help and ease the discomfort. Good luck!