Please help!!!

So my boyfriend and i have been dating a while and we’ve been having sex for around 2 months and everything was great. But more recently, whenever he would first put it in, the first few strokes would hurt like hell!! After a while the pain would go away and i would feel fine. But today when he was putting it in, i literally could not go past the tip it hurt so bad. We’ve had sex before and i was not a virgin before i met him. We are always well lubricated before we do anything so i cant think of any other reasons for this..... any thoughts????? Anything helps!!