Painful Sex

My boyfriend and I are no strangers to sex, but lately, over the past month or two, it’s become incredibly painful for me. Before this I’d had no problems. We foreplay for at least half an hour, usually over forty minutes with a mixture of penetrative and nonpenetrative foreplay. We’ve been using water based lube to try and help but it’s difficult as using one brand burns no matter how much is used, with another burning if a moderate to large amount is used. It’s starting to get unbearable and I’m all out of ideas. Usually we stick to doggy, missionary, and cowgirl as anything else hurts too much and these offer the least effort (because painful sex is draining), and the offer me more control which helps to a degree with the pain. We don’t use condoms, we’re both STD clear, and I’ve had the contraceptive implant since May 2016 so birth control is unlikely to be interfering with it. PLEASE could somebody help suggest something? I’m desperate at this point