chapped/cracked vaginal entrance for a while

Hi, I've been having these cracks on my vagina for a while. They appear always at the beginning of every intercourse, it burns, stings, my vag is too warm, even hot, but only during intercourse. I dont have any problems/symptoms during day, neither discharge. They always heal and then appear again. My gyn told me to buy multigyn to regenerate it down there so I was applying the gel for 30 days (its written there that you shouldnt use it more), then I had sex with my boyfriends but it still wasnt the best. Now we had sex after 2 weeks and it cracked again. Is it some STD/infection? + im on birth control since february/march and this happens since mid july + we are using durex naturals lube and its always the same

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