The most likely cause of your symptoms is chronic/recurrent yeast infection, or irritant vaginitis (more likely, I think). Vaginitis just means inflammation of the vaginal/vulvar area.
I'm not sure if you've been examined, or have had swabs and had yeast ruled out. If it is yeast, it may be easily treated with an anti-fungal. But some women get recurrent infections that leave when treated and come back, or never fully resolve- sometimes they have yeast that is resistant to the typically used anti-yeast treatments.
Because you didn't mention related discharge, and because it comes at the same time every month, this makes me think that it is more likely irritant vaginits (although you can have yeast without notieable discharge, and it would probably be hard to tell since you are on your period anyway). It is common that recurrent burning/itching is wrongly diagnosed as yeast when it is due to irritation from something you are coming in contact with. Often things present in creams, lubricants, spermicides, scented sanitary products, douches, soaps, bubble baths and condom lubricants can be cause symptoms like yours.
Try to be particular about figuring out if there is something that you are coming in contact with each month- most like a pad or scented spray or something. If you eliminate that possibility, you should see a Gynecologist for an exam to rule out yeast and other skin disorders.
I was experiencing problems with Candida Yeast infection and it coming back all the time. It's been ahwil since I have ha any symptoms of a yeast infections. Every once in awhile I will get some discharge with a smelly odour. I had to take a pill once a month from the doctor to treat it along with suppositories.. Sex was too painful as well and so it's been about a year that this has been going on. I went to a gynecologist yesturday and he said that he didn't see any infection at all and thinks that the infection is gone. But it still burns and is really uncomfortable at that time of month. And it is still very painful when it comes to sex. So he thinks that the pain I feel during sex is just in my head and that I tense up and tighten up down there because of all the pain that I had experienced at the beginning of this infection. Does that make sense?
It's certainly possible that the pain you're having during sex could be caused, or at least made worse, by the anticipation that it's going to be painful. But it also sounds like you are having burning and pain during your period aside from during sex.
I still think it's possibly a contact-irritation thing, especially if your doctor said you don't have an infection. Hopefully you will find that it is something like that, that you can change and notice a big improvement.
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