Very embarrassing question

I feel so stupid even typing this, and I'm sure some will even think this is fake or trolling or something, but I assure you it isn't. This a very real and very humiliating question, and I'm glad the internet exists so I can ask this relatively anonymously.
OK, here goes.
Gay guys, ummmm, how do you do it?
Sex I mean. I have tried a number of times to have anal sex with men and I just can't do it. I'm super turned on. The guys are attractive. They're all more expereienced than me. I know about lube. Hell, I even use viagra though I'm not sure I need to.
But it's been a fail every time. I literally CAN'T GET IT IN. I see guys in porn and they just *WHOOSH* and it goes right in. To me it feels like every single guy I'm with is clenching their butthole to make it impassible. It feels like trying to fuck a wall, and I have no idea what the hell I can possibly be doing wrong. I've tried different positions, but nothing works and I'm almost to the point of giving up completely. Last night was particularly demeaning because the guy berated me after and I felt like.....garbage. I'm crying as I type this.
Please help.