Why does hymen burn when i have sex?

My boyfriend and I had sex about 10 times in a course of three days with no problem. We were both virgins. Just a little pain going in for the first few seconds then it was amazing. No pain. Now We try and it burns. We tried a new lube this time. Before We used ky and it was fine. Now We bought the equate brand from Walmart. Maybe I'm allergic to it. I'm tired of the burning I want sex again.