You are asking questions which cannot be answered without a thorough exam. Have you seen a gynecologist? You need to see one ASAP and describe ALL your symptoms, as you've detailed them in this post. There are so many possibilities, too numerous to list here--including yeast infections, STDs, etc.
However, it's also possible that you're having involuntary tightening of your vaginal muscles due to stress, fear, anxiety or some other reason. If this is true, this can create lots of pain.
If you don't have a gynecologist, go to your nearest Planned Parenthood or women's clinic for an exam. They're frequently low-cost, confidential and likely to provide you with excellent care as well as the opportunity to talk about this issue. If there's no physiological cause, it's likely there are some emotional issues such as those discussed above. In that case, you might want to see a counselor who is trained to help women with sexual concerns. Best of luck to you. Dr. J