Hi. Every time I ejaculate my sperm feels like it's getting blocked right before it slowly comes out. It began last week when I masturbated backtoback?

That's fine. No two guys have quite the same sensations before they ejaculate, and it even varies with health, quantity of semen, and medications. You may have a small temporary stricture from a mucosal tear at the outlet of a seminal vesicle from overdoing things -- this is hypothetical and should self-cure. If you're ejaculating and it feels nice, stop worrying and enjoy the experience. Best wishes.