What Causes Burning Sensation In The Vagina During Intercourse?

Hi I fell pregnant in 2015 and delivered January 2016 at 32weeks baby only lived for 4months she had an unknown lung infection that couldn t get cured, I used the 3 months contraceptive injection after delivery , I only used it once then I switched to oral contraceptives until January 2017 however while using the oral contraceptives I use to see my periods but after I had stopped using them my periods have never came back. I started feeling nausea and had tender breasts and discharge came out of the breasts , went to see the doc had a pregnancy test and came out negative he did an ultra sound scan and found that I had a cyst and treated me , however the antibiotics he gave me caused a yeast infection in my vagina he again treated that but I am still not seeing my periods and every time I have intercourse with my husband it is painful and there is a burning sting in my vagina when I pee after having the intercourse I also see brown flakes when I wipe my vagina and my bums.