Is he cheating

Hey ladies. So for the past couple days, since the last time I had sex with my boyfriend I noticed something. A day after I had this weird burning soreness inside my vagina. It was only sore and had that feeling if I put a finger in it or had sex. I haven’t had sex with any other man and we don’t use condoms. I randomly got this very bad burning when I went to use thats caness balance PH balance tubes you squirt in there thinking maybe that is why... the burning is slowly going away.. does anyone else have this? Vaginal dryness , not drinking enough water? Or is he cheating and gave me and STD?