Why is it still happening?😫

I’ve been going out with my boyfriend for 2 years and every SINGLE time we have sex, it’s so sore when he first starts to enter me, due to his size I’m guessing? At first we thought it was from lack of lubrication but we tried lubes and everything and even if he goes slow it’s just so sore til I get used to it ! I really don’t know what to do about it, is there even anything I can do ?