Birth Control Pills Causing Vaginal Itching/burning?

So I've been sexually active with the same partner for a year and a half. Recently the area around my vaginal opening has been real itchy, and after I have sex it burns down there for like an hour (kind-of like it would if you had real rough sex). This happened to me once before about 6 months ago, except I gave into the temptation to scratch the itch, and it only made it worse, and everything got all raw and painful down there. I went to the gyno and she gave me a monstat and anti-bacterial cream. Neither of which worked. The only thing that helped even a little was hydrocortisone. However, I changed birth control from the pill (Loestrin Fe) to the depo shot. The itching went away. Was on the shot for like 6 months and couldn't stand it, so I switched back to the same pill two months ago and now the itching has returned. I did not read anything about itching on the side-effects of this birth control, does anyone know what the deal is?
 
Things I know that it's not, so please don't suggest them.
 
Yeast Infection
-No smell or discharge.
-Monistat doesn't help.
-Itching on the outside NOT inside of my vagina.
 
STD
-Me and my partner are both clean and yes, I know that for a fact.
 
Sperm Allergy
-I never use condoms and have never had a problem, either vaginally or orally. 
 
Also, I do not use any soaps to wash down there, only water, so it shouldn't be a chemical allergy either.