Painful sex

My boyfriend now is the best sex I’ve ever had. But sometimes I struggle getting comfortable. I’ve never had an issue before, but with him sometimes it hurts so much that we have to stop. The more sex we have the worse it is. Sometimes I can work through it and get comfortable but after sex 3 days in a row, it will hurt so bad we cant even attempt it anymore. I’m very turned on and definitely want it so I’m not sure why my body is reacting this way. We have tried lube... it only helps some of the time... I’m getting super frustrated with myself, so any advice or guesses as to why this could be happening is GREATLY appreciated.