Only time I don't have burning is when on period. Why?

Hi:
I am new here, but not to vulvodynia. Have had it off and on for 5-6 years. For whatever reason, or for no reason it really hasn't been a problem much in the past year.  
Here is my pattern over the past year:  Ok all month, then on the last day of period, with tail end of bleeding I will get burning for 1-2 days. Then I will be ok.
Here is my pattern now: BURN ALL DAY!  Urine and whatever discharge that is coming out of me is what provokes the burning. Better when I sleep at night as I lay flat and less discharge comes out.  Vaginal and urine cultures are all normal. Vagina looks red, but discharge is normal and not smelly etc. Total mystery.

Here is the bigger mystery:
When I get my period, I mean the minute I start to bleed until I get to the tail end of it, I have NO burning.  WHY? If I could figure out what about my period stops the burning on the spot that would be good as maybe I can figure out what my body is needing.  Does anybody know what happens to the ph, vaginal flora etc during the period? What might be in the blood that soothes my vagina?
I am 48 and sure I am in perimenopause, but still have regular periods. I have also had Interstitial Cystitis for 10 years, lucky me.  Just really want to die at this point.  Ready to give up. Crying all day, can't leave the house. Have two kids who need me…

If you have any thoughts about why my period might alleviate my symptoms for a few days while on it I would be most grateful!

Just a few guesses -

Blood is slightly alkaline, whereas urine tends to be somewhat acidic. So the blood will reduce the acidity of your urine. Also, I would guess the blood is also acting to dilute any urine, and to form a bit of a barrier. You may want to try a low oxalate diet as oxalate crystals in your urine could be causing the burning pain and also triggering histamine release which leads to redness, burning, and possibly itching. The diet can take some time to really make a difference as things need to calm down. If your problem has been long standing, then you may also have pelvic floor muscle dysfunction from tightening up due to the pain. Then physio and pelvic floor exercises may be needed, in addition to the diet. In the meantime, try peeing while squirting water on the area to dilute urine when not on your period. At 48, you may be starting to have symptoms due to low estrogen. Good luck finding a doctor to help with that! A naturopath may be an option. Low estrogen can cause all sorts of bladder problems, as well as vulvar pain. (I am 52, so I can sympathize with your situation.)

I had to deal with my issues by handling yeast (probiotics and low carb diet), oxalates (low oxalate diet and calcium citrate), and finally physio, simultaneously. Trying them individually over the years did not help. I had to do them all together to get some relief.

I hope you get some relief soon!

Thank you very much for your helpful reply. Having had this for so many years, I did try to the low oxalate diet. Don't recall how long I did it for, but it for sure didn't seem to help. It was so long ago. Maybe worth a try again. I tend to be on the thin side and like to weigh more, so I hate doing any kind of diets that restrict my food and I already follow the IC diet more or less and have for years.
I like your idea of using water when I pee to dilute the urine. I will try that with a spray bottle of some sort. I have done PT and it only made me worse, especially internal work.
I really appreciate your thinking about my mystery situation of my periods helping! It was very informative, your reply..
Thank you and all the best.

Hi. I had a flare-up some years ago with symptoms different from yours - severe swelling and tearing rather than a burning feeling - but I also noticed that everything stopped while I was on my period, only to get start again afterwards. I had always hypothesized it was something in my discharge, or similarly something with my flora, etc. No probiotics or antibiotics or anti-yeast medicine ever worked, however. I'm currently in the middle of another episode and waiting for my period to begin to see if I can get some relief or if the same pattern will emerge. In doing research this time around, I've noticed some people online have discussed hormonal triggers, for example being on birth control and suffering from low levels of estrogen. Some of these individuals have gone off their birth control or used a compound estrogen/testosterone cream to treat the area. It's just a lead but, perhaps these hormonal fluctuations during your cycle may be something to look into with your doctor.