Hi thanks for your question.
You are suffering from a problem called as vaginismus
In vaginismus the muscles of vagina contract or go into spasm in response to attemted insertion of penis.Since this occur without the conscious intent or conscent of women it can be very perplexing.
Usually at the root of vaginismus is a combination of physical or non physical (psychiological) triggers that causes the body to respond to anticipated pain.by tightening the vaginal muscle.The list of causes of vaginismus is very long.The most common being,anxiety
,partener problem (this doesn't hold good for you),trauma,guilt,fear of getting pregnant,fear of pain and finally no cause at all.
I would suggest you to consult a gynaecologist to rule out any physicial cause of vaginismis.
Consultation with a psychiologist is also advisible to rule out any psychological cause.
Treatment involves progressive desenitization excercises.These excercise help women to learn to control and relax pelvic floor
around vagina.These excercises can be done at home and one of common excercise is called as Kegel excercise.
I would suggest you to learn these excercises from gynaecologist.He/she may also advice you,how to manage your problem.
Hope this answers your question.