6 yeast infections in 6 months

hi everyone, for the past 6 months ive been sexually active with my new boyfriend. about once a month at a ny certain time with no pattern ive been getting yeast infections. we both came from a relationship were neither of us were having sex for quite a few years so needless to say we were having sex alot. before us i only had a yeast infection a couple times in life. the crazy part is i thought i had another and i used monistat 7 day. but after completing it i still saw white discharge and though i still had it. but ive had 3 diffrent swab cultures and everything came back negative for yeast and BV. we had sex about 2 weeks after treatment and i was still very sore on the inside. and now even 17 days after i used the monistat ive still got a sore red ring around my vaginal opening that the dr. gave me a estrogen cream for… have any of you been this sore this long after treatment? im scared the tests wernt correct? im aslo scared im going to be stuck in this pattern of getting yeast infections. its very depressing having this issue being in a new relationship as you all know very well im sure.